James Fowler

PUBLICATIONS

1. Current, Future and Potential Use of Mobile and Wearable Technologies and Social Media Data in the ABCD Study to Increase Understanding of Contributors to Child Health Mobile and wearable technologies and novel methods of data collection are innovating health-related research. These technologies and methods allow for multi-system level capture of data across environmental, physiological, behavioral, and psychological domains. In the Adolescent Brain Cognitive Development (ABCD) Study, there is great potential for harnessing the acceptability, accessibility, and functionality of mobile and social technologies for in-vivo data capture to precisely measure factors, and interactions between factors, that contribute to childhood and adolescent neurodevelopment and psychosocial and health outcomes. Here we discuss advances in mobile and wearable technologies and methods of analysis of geospatial, ecologic, social network and behavioral data. Incorporating these technologies into the ABCD study will allow for interdisciplinary research on the effects of place, social interactions, environment, and substance use on health and developmental outcomes in children and adolescents.

   Kara Bagot, Stephen Matthews, Michael Mason, Lindsay Squeglia, James H. Fowler, Kevin Gray, Megan Herting, April May, Ian Colrain, Job Godino, Susan Tapert, Sandra Brown, Kevin Patrick
   Developmental Cognitive Neuroscience 32 (4): 121–129 (August 2018)

2. Egocentric Networks and Physical Activity Outcomes in Latinas Objective
   Despite data linking the social environment to physical inactivity in Latinas, research on social network predictors of physical activity (PA) is limited. This study examined social network predictors of PA change in Latinas.
   Methods
   Egocentric network data were collected from 102 adult Latinas (egos) participating in a randomized controlled PA intervention trial for underactive women. Moderate-to-vigorous PA (MVPA) was measured in minutes per week using the 7-Day PA Recall Interview and accelerometers at baseline and 12 months. Analyses characterized social network structure, composition, tie strength, homogeneity, and support for PA and determined the relationship between network characteristics and PA outcomes.
   Results
   Networks had an average of four social ties (alters). Networks were high in density and transitivity and low in components, indicating high cohesion. Networks were primarily composed of females, Latinos, Spanish-speakers, and family members. Relationship ties were strong as evidenced by close living proximity, in-person contact, high emotional closeness, and long relationship duration. There was high homogeneity in demographics and PA behaviors. Multivariate analyses revealed that network size, familial ties, contact frequency, and ego-alter dissimilarities in age and running but similarities in walking, were associated with increased MVPA. Networks high in support for PA in the form of complimenting ego on exercise, taking over chores to allow ego to exercise, and co-participating with ego in exercise were also associated with greater MVPA.
   Conclusion
   These findings contribute to better understanding interpersonal processes that may influence behavior change in a group with especially low levels of PA.

   Becky Marquez, Gregory J. Norman, James H. Fowler, Kim Gans, Bess Marcus
   PLOS ONE 13 (6): e0199139 (18 June 2018)

3. Weather Impacts Expressed Sentiment We conduct the largest ever investigation into the relationship between meteorological conditions and the sentiment of human expressions. To do this, we employ over three and a half billion social media posts from tens of millions of individuals from both Facebook and Twitter between 2009 and 2016. We find that cold temperatures, hot temperatures, precipitation, narrower daily temperature ranges, humidity, and cloud cover are all associated with worsened expressions of sentiment, even when excluding weather-related posts. We compare the magnitude of our estimates with the effect sizes associated with notable historical events occurring within our data.

   Patrick Baylis, Nick Obradovich, Yury Kryvasheyeu, Haohui Chen, Lorenzo Coviello, Esteban Moro, Manuel Cebrian, James H. Fowler
   PLOS ONE 13 (4): e0195750 (25 April 2018)

4. Weight and Weight Control Behaviors of Latinas and Their Social Ties Objective: Shared behaviors have been implicated in the clustering of obesity among socially connected people. This study determined how weight and weight control behaviors of participants and their social ties are related and how these factors are associated with weight change in participants. Method: Adult Latinas participating in a lifestyle intervention completed an egocentric network measure of weight and weight control behaviors. Participant weight was objectively measured at baseline and 12 months. Multivariable regression models determined the relationship between weight and weight control behaviors of participants and their social ties. Results: Participants and their social ties shared similarities in weight control behaviors and weight change. Participants who reported social ties that had lost weight were more likely to eat small portions and low-fat foods, but those with social ties that had gained weight were more likely to use herbal supplements. Participants who reported more social ties who exercised, drank liquid meal replacements, took herbal supplements, and self-weighed were more likely to lose weight whereas those with fewer social ties that exercised were more likely to gain weight. Weight loss and weight gain by social ties predicted participant weight loss and weight gain, respectively. Conclusions: Given that weight and weight control behaviors of Latinas reflect that of their social ties, targeting existing social networks for lifestyle interventions may more effectively improve and sustain health-promoting behaviors and outcomes.

   Becky Marquez, Gregory J. Norman, James H. Fowler, Kim Gans, Bess Marcus
   Health Psychology 37 (4): 318–325 (April 2018)

5. Familial Social Structure and Socially Driven Genetic Differentiation in Hawaiian Short-Finned Pilot Whales Social structure can have a significant impact on divergence and evolution within species, especially in the marine environment, which has few environmental boundaries to dispersal. On the other hand, genetic structure can affect social structure in many species, through an individual preference towards associating with relatives. One social species, the short-finned pilot whale (Globicephala macrorhynchus), has been shown to live in stable social groups for periods of at least a decade. Using mitochondrial control sequences from 242 individuals and single nucleotide polymorphisms from 106 individuals, we examine population structure among geographic and social groups of short-finned pilot whales in the Hawaiian Islands, and test for links between social and genetic structure. Our results show that there are at least two geographic populations in the Hawaiian Islands: a Main Hawaiian Islands (MHI) population and a Northwestern Hawaiian Islands/Pelagic population (FST and ΦST p < .001), as well as an eastern MHI community and a western MHI community (FST p = .009). We find genetically driven social structure, or high relatedness among social units and clusters (p < .001), and a positive relationship between relatedness and association between individuals (p < .0001). Further, socially organized clusters are genetically distinct, indicating that social structure drives genetic divergence within the population, likely through restricted mate selection (FST p = .05). This genetic divergence among social groups can make the species less resilient to anthropogenic or ecological disturbance. Conservation of this species therefore depends on understanding links among social structure, genetic structure and ecological variability within the species.

   Amy M. Van Cise, Karen K. Martien, Sabre D. Mahaffy, Robin W. Baird, Daniel L. Webster, James H. Fowler, Erin M. Oleson, Phillip A. Morin
   Molecular Ecology 26 (23): 6730–6741 (December 2017)

6. Digit Ratio (2D:4D) and Social Integration: An Effect of Prenatal Sex Hormones The position people occupy in their social and professional networks is related to their social status and has strong effects on their access to social resources. While attainment of particular positions is driven by behavioral traits, many biological factors predispose individuals to certain behaviors and motivations. Prior work on exposure to fetal androgens (measured by second-to-fourth digit ratio, 2D:4D) shows that it correlates with behaviors and traits related to social status, which might make people more socially integrated. However, it also predicts certain anti-social behaviors and disorders associated with lower socialization. We explore whether 2D:4D correlates with network position later in life and find that individuals with low 2D:4D become more central in their social environment. Interestingly, low 2D:4D males are more likely to exhibit high betweenness centrality (they connect separated parts of the social structure), while low 2D:4D females are more likely to exhibit high in-degree centrality (more people name them as friends). These gender-specific differences are reinforced by transitivity (the likelihood that one's friends are also friends with one another): neighbors of low 2D:4D men tend not to know each other; the contrary is observed for low 2D:4D women. Our results suggest that biological predispositions influence the organization of human societies and that exposure to prenatal androgens influences different status seeking behaviors in men and women.

   Jaromír Kovářík, Pablo Brañas-Garza, Michael W. Davidson, Dotan A. Haim, Shannon Carcelli, James H. Fowler
   Network Science 5 (4): 476–489 (December 2017)
   • Supplementary Appendix

7. Core-Periphery Structure in Networks (Revisited) Intermediate-scale (or "meso-scale") structures in networks have received considerable attention, as the algorithmic detection of such structures makes it possible to discover network features that are not apparent either at the local scale of nodes and edges or at the global scale of summary statistics. Numerous types of meso-scale structures can occur in networks, but investigations of such features have focused predominantly on the identification and study of community structure. In this paper, we develop a new method to investigate the meso-scale feature known as core-periphery structure, which entails identifying densely connected core nodes and sparsely connected peripheral nodes. In contrast to communities, the nodes in a core are also reasonably well-connected to those in a network's periphery. Our new method of computing core-periphery structure can identify multiple cores in a network and takes into account different possible core structures. We illustrate the differences between our method and several existing methods for identifying which nodes belong to a core, and we use our technique to examine core-periphery structure in examples of friendship, collaboration, transportation, and voting networks. For this new SIGEST version of our paper, we also discuss our work's relevance in the context of recent developments in the study of core-periphery structure.

   Puck Rombach, Mason A. Porter, James H. Fowler, Peter J. Mucha
   SIAM Review 59 (3): 619–646 (7 August 2017)

8. Nighttime Temperature and Human Sleep Loss in a Changing Climate Human sleep is highly regulated by temperature. Might climate change—through increases in nighttime heat—disrupt sleep in the future? We conduct the inaugural investigation of the relationship between climatic anomalies, reports of insufficient sleep, and projected climate change. Using data from 765,000 U.S. survey respondents from 2002 to 2011, coupled with nighttime temperature data, we show that increases in nighttime temperatures amplify self-reported nights of insufficient sleep. We observe the largest effects during the summer and among both lower-income and elderly respondents. We combine our historical estimates with climate model projections and detail the potential sleep impacts of future climatic changes. Our study represents the largest ever investigation of the relationship between sleep and ambient temperature and provides the first evidence that climate change may disrupt human sleep.

   Nick Obradovich, Robyn Migliorini, Sara C. Mednick, James H. Fowler
   Science Advances 2 (3): e1601555 (26 May 2017)
   • Supplementary Appendix
   • New York Times
   • Washington Post

9. Social Influence and Political Mobilization: Further Evidence from a Randomized Experiment in the 2012 U.S. Presidential Election A large-scale experiment during the 2010 U.S. Congressional Election demonstrated a positive effect of an online get-out-the-vote message on real world voting behavior. Here, we report results from a replication of the experiment conducted during the U.S. Presidential Election in 2012. In spite of the fact that get-out-the-vote messages typically yield smaller effects during high-stakes elections due to saturation of mobilization efforts from many sources, a significant increase in voting was again observed. Voting also increased significantly among the close friends of those who received the message to go to the polls, and the total effect on the friends was likely larger than the direct effect, suggesting that understanding social influence effects is potentially even more important than understanding the direct effects of messaging. These results replicate earlier work and they add to growing evidence that online social networks can be instrumental for spreading offline behaviors.

   Jason J. Jones, Robert M. Bond, Eytan Bakshy, Dean Eckles, James H. Fowler
   PLOS ONE 12 (4): e0173851 (26 April 2017)
   • Supporting Information

10. Climate Change May Alter Human Physical Activity Patterns Regular physical activity supports healthy human functioning. Might climate change - by modifying the environmental determinants of human physical activity - alter exercise rates in the future? Here we conduct an empirical investigation of the relationship between meteorological conditions, physical activity and future climate change. Using data on reported participation in recreational physical activity from over 1.9 million US survey respondents between 2002 and 2012, coupled with daily meteorological data, we show that both cold and acutely hot temperatures, as well as precipitation days, reduce physical activity. We combine our historical estimates with output from 21 climate models and project the possible physical activity effects of future climatic changes by 2050 and 2099. Our projection indicates that warming over the course of this century may increase net recreational physical activity in the United States. Activity may increase most during the winter in northern states and decline most during the summer in southern states.

    Nick Obradovich, James H. Fowler
    Nature Human Behaviour 1: 0097 (24 April 2017)
    • Supplementary Appendix
    • New York Times

11. Dueling Biological and Social Contagions Numerous models explore how a wide variety of biological and social phenomena spread in social networks. However, these models implicitly assume that the spread of one phenomenon is not affected by the spread of another. Here, we develop a model of “dueling contagions”, with a particular illustration of a situation where one is biological (influenza) and the other is social (flu vaccination). We apply the model to unique time series data collected during the 2009 H1N1 epidemic that includes information about vaccination, flu, and face-to-face social networks. The results show that well-connected individuals are more likely to get vaccinated, as are people who are exposed to friends who get vaccinated or are exposed to friends who get the flu. Our dueling contagion model suggests that other epidemiological models may be dramatically underestimating the R0 of contagions. It also suggests that the rate of vaccination contagion may be even more important than the biological contagion in determining the course of the disease. These results suggest that real world and online platforms that make it easier to see when friends have been vaccinated (personalized vaccination campaigns) and when they get the flu (personalized flu warnings) could have a large impact on reducing the severity of epidemics. They also suggest possible benefits from understanding the coevolution of many kinds of dueling contagions.

    Feng Fu, Nicholas A. Christakis, James H. Fowler
    Scientific Reports 7: 43634 (2 March 2017)

12. Exploiting Social Influence to Magnify Population-Level Behaviour Change in Maternal and Child Health: Study Protocol for a Randomised Controlled Trial of Network Targeting Algorithms in Rural Honduras Introduction
    Despite global progress on many measures of child health, rates of neonatal mortality remain high in the developing world. Evidence suggests that substantial improvements can be achieved with simple, low-cost interventions within family and community settings, particularly those designed to change knowledge and behaviour at the community level. Using social network analysis to identify structurally influential community members and then targeting them for intervention shows promise for the implementation of sustainable community-wide behaviour change.
    
    Methods and analysis
    We will use a detailed understanding of social network structure and function to identify novel ways of targeting influential individuals to foster cascades of behavioural change at a population level. Our work will involve experimental and observational analyses. We will map face-to-face social networks of 30,000 people in 176 villages in Western Honduras, and then conduct a randomised controlled trial of a friendship-based network-targeting algorithm with a set of well-established care interventions. We will also test whether the proportion of the population targeted affects the degree to which the intervention spreads throughout the network. We will test scalable methods of network targeting that would not, in the future, require the actual mapping of social networks but would still offer the prospect of rapidly identifying influential targets for public health interventions.
    
    Ethics and dissemination
    The Yale IRB and the Honduran Ministry of Health approved all data collection procedures (Protocol number 1506016012) and all participants will provide informed consent before enrolment. We will publish our findings in peer-reviewed journals as well as engage non-governmental organisations and other actors through venues for exchanging practical methods for behavioural health interventions, such as global health conferences. We will also develop a 'toolkit' for practitioners to use in network-based intervention efforts, including public release of our network mapping software.
    
    Trial registration number NCT02694679; Pre-results.

    Holly B. Shakya, Derek Stafford, D. Alex Hughes, Thomas Keegan, Rennie Negron, Jai Broome, Mark McKnight, Liza Nicoll, Jennifer Nelson, Emma Iriarte, Maria Ordonez, Edo Airoldi, James H. Fowler, Nicholas A. Christakis
    BMJ Open 7 (3): e012996 (March 2017)

13. The Paradox of Weak Ties in 55 Countries People find jobs through their social networks using ties of different strengths. Intuitively weak ties might be less useful because people communicate less often with them, or more useful because they provide novel information. Granovetter's early work showed that more job-seekers get help via acquaintances than friends (Granovetter, 1973). However, recent work on job-finding (Gee et al., 2017) shows an apparent paradox of weak ties in the United States: most people are helped through one of their numerous weak ties, but a single stronger tie is significantly more valuable at the margin. Although some studies have addressed the importance of weak ties in job finding within specific countries, this is the first paper to use a single dataset and methodology to compare the importance of weak ties across countries. Here, we use de-identified data from almost 17 million social ties in 55 countries to document the widespread existence of this paradox of weak ties across many societies. More people get jobs where their weak ties work. However, this is not because weak ties are more helpful than strong ties – it is because they are more numerous. In every country, the likelihood of going to work where an individual friend works is increasing – not decreasing – with tie strength. Yet, there is substantial variation in the added value of a strong tie at the margin across these countries. We show that the level of income inequality in a country is positively correlated with the added value of a strong tie, so that individual strong ties matter more when there is greater income inequality.

    Laura K. Gee, Jason J. Jones, Christopher J. Fariss, Moira Burke, James H. Fowler
    Journal of Economic Behavior and Organization 133: 362–372 (January 2017)

14. Face-to-Face and Online Networks: College Students' Experiences in a Weight-Loss Trial This study aimed to understand how college students participating in a 2-year randomized controlled trial (Project SMART: Social and Mobile Approach to Reduce Weight; N = 404) engaged their social networks and used social and mobile technologies to try and lose weight. Participants in the present study (n = 20 treatment, n = 18 control) were approached after a measurement visit and administered semi-structured interviews. Interviews were analyzed using principles from grounded theory. Treatment group participants appreciated the timely support provided by the study and the integration of content across multiple technologies. Participants in both groups reported using non-study-designed apps to help them lose weight, and many participants knew one another outside of the study. Individuals talked about weight-loss goals with their friends face to face and felt accountable to follow through with their intentions. Although seeing others' success online motivated many, there was a range of perceived acceptability in talking about personal health-related information on social media. The findings from this qualitative study can inform intervention trials using social and mobile technologies to promote weight loss. For example, weight-loss trials should measure participants' use of direct-to-consumer technologies and interconnectivity so that treatment effects can be isolated and cross-contamination accounted for.

    Gina Merchant, Nadir Weibel, Laura Pina, William G. Griswold, James H. Fowler, Guadalupe X. Ayala, Linda C. Gallo, James Hollan, Kevin Patrick
    Journal of Health Communication 22 (1): 75–83 (January 2017)
    • Supplementary Appendix

15. An Exploratory Comparison of Name Generator Content: Data From Rural India Since the 1970s sociologists have explored the best means for measuring social networks, although few name generator analyses have used sociocentric data or data from developing countries, partly because sociocentric studies in developing countries have been scant. Here, we analyze 12 different name gen- erators used in a sociocentric network study conducted in 75 villages in rural Karnataka, India. Having unusual sociocentric data from a non-Western context allowed us to extend previous name generator research through the unique analyses of network structural measures, an extensive consideration of homophily, and investigation of status difference between egos and alters. We found that domestic interaction questions generated networks that were highly clustered and highly centralized. Similarity between respondents and their nominated contacts was strongest for gender, caste, and religion. We also found that domestic interaction name generators yielded the most homogeneous ties, while advice questions yielded the most heterogeneous. Participants were generally more likely to nominate those of higher social status, although certain questions, such as who participants talk to uncovered more egalitarian relationships, while other name generators elicited the names of social contacts distinctly higher or lower in status than the respondent. Some questions also seemed to uncover networks that were specific to the cultural context, suggesting that network researchers should balance local relevance with global generalizability when choosing name generators.

    Holly B. Shakya, Nicholas A. Christakis, James H. Fowler
    Social Networks 23: 157–168 (January 2017)
    • Supplementary Appendix

16. Social Endorsement Cues and Political Participation Which individuals are most responsive to get-out-the-vote (GOTV) messages that emphasize the social aspects of voting? Recent literature has shown that GOTV messages that emphasize the social environment in which an individual is embedded are particularly effective at increasing voting rates. Until now, we have not had good estimates for the types of people for whom social GOTV messages are most effective. We report a new set of disaggregated results of a randomized controlled trial of political mobilization messages delivered to 61 million Facebook users during the 2010 U.S. Congressional elections. The results suggest that social endorsement cues are differentially effective for different types of political behaviors—political expression, information seeking, and voting—and for different kinds of people, based on both demographic and social characteristics, raising new questions about the mechanisms explaining social pressure effects.

    Robert M. Bond, Jaime E. Settle, Christopher J. Fariss, Jason J. Jones, James H. Fowler
    Political Communication 34 (2): 261–281 (2017)
    • Supplementary Appendix

17. Reimagining Human Research Protections for 21st Century Science Background
    Evolving research practices and new forms of research enabled by technological advances require a redesigned research oversight system that respects and protects human research participants.
    
    Objective
    Our objective was to generate creative ideas for redesigning our current human research oversight system.
    
    Methods
    A total of 11 researchers and institutional review board (IRB) professionals participated in a January 2015 design thinking workshop to develop ideas for redesigning the IRB system.
    
    Results
    Ideas in 5 major domains were generated. The areas of focus were (1) improving the consent form and process, (2) empowering researchers to protect their participants, (3) creating a system to learn from mistakes, (4) improving IRB efficiency, and (5) facilitating review of research that leverages technological advances.
    
    Conclusions
    We describe the impetus for and results of a design thinking workshop to reimagine a human research protections system that is responsive to 21st century science.

    Cinnamon Bloss, Camille Nebeker, Matthew Bietz, Deborah Bae, Barbara Bigby, Mary Devereaux, James Fowler, Ann Waldo, Nadir Weibel, Kevin Patrick, Scott Klemmer, Lori Melchar
    Journal of Medical Internet Research 18 (12): e329 (December 2016)

18. Online Social Integration Is Associated with Reduced Mortality Risk Social interactions increasingly take place online. Friendships and other offline social ties have been repeatedly associated with human longevity, but online interactions might have different properties. Here, we reference 12 million social media profiles against California Department of Public Health vital records and use longitudinal statistical models to assess whether social media use is associated with longer life. The results show that receiving requests to connect as friends online is associated with reduced mortality but initiating friendships is not. Additionally, online behaviors that indicate face-to-face social activity (like posting photos) are associated with reduced mortality, but online-only behaviors (like sending messages) have a nonlinear relationship, where moderate use is associated with the lowest mortality. These results suggest that online social integration is linked to lower risk for a wide variety of critical health problems. Although this is an associational study, it may be an important step in understanding how, on a global scale, online social networks might be adapted to improve modern populations' social and physical health.

    William R. Hobbs, Moira Burke, Nicholas A. Christakis, James H. Fowler
    PNAS 113 (46): 12980–12984 (15 November 2016)
    • Supplementary Appendix
    • New York Times
    • Los Angeles Times
    • UCSD Press Release

19. Formation of Raiding Parties for Intergroup Violence is Mediated by Social Network Structure Intergroup violence is common among humans worldwide. To assess how within-group social dynamics contribute to risky, between-group conflict, we conducted a 3-y longitudinal study of the formation of raiding parties among the Nyangatom, a group of East African nomadic pastoralists currently engaged in small-scale warfare. We also mapped the social network structure of potential male raiders. Here, we show that the initiation of raids depends on the presence of specific leaders who tend to participate in many raids, to have more friends, and to occupy more central positions in the network. However, despite the different structural position of raid leaders, raid participants are recruited from the whole population, not just from the direct friends of leaders. An individual's decision to participate in a raid is strongly associated with the individual's social network position in relation to other participants. Moreover, non-leaders have a larger total impact on raid participation than leaders, despite leaders' greater connectivity. Thus, we find that leaders matter more for raid initiation than participant mobilization. Social networks may play a role in supporting risky collective action, amplify the emergence of raiding parties, and hence facilitate intergroup violence in small-scale societies.

    Luke Glowacki, Alexander Isakov, Richard W. Wrangham, Rose McDermott, James H. Fowler, Nicholas A. Christakis
    PNAS 113 (43): 12114–12119 (25 October 2016)
    • Supplementary Appendix
    • Supplementary Tables

20. Timing Matters: How Social Influence Affects Adoption Pre- and Post-Product Release Social influence is typically studied after a product is released. Yet, audience expectations and discussions begin before a product's release. This observation suggests a need to understand adoption processes over a product's life cycle. To explore pre- and postrelease social influence processes, this article uses survey data from Americans exposed to word of mouth for 309 Hollywood movies released over two and a half years. The data suggest pre- and postrelease social influences operate differently. Prerelease social influence displays a critical transition point with relation to adoption: before a critical value, any level of social influence is negligibly related to adoption, but after the critical value, the relationship between social influence and adoption is large and substantive. In contrast, postrelease social influence exhibits a positive linear relationship with adoption. Prerelease social influence is argued to require more exposures than postrelease social influence because of differences in the diagnosticity and accessibility of the information. To complement the survey data, computational models are used to test alternative hypotheses. Evidence from the computational models supports the proposed model of social influence.

    Sara B. Soderstrom, Brian Uzzi, Derek D. Rucker, James H. Fowler, Daniel Diermeier
    Sociological Science 3: 915–939 (October 2016)
    • Supplementary Appendix

21. Using Social and Mobile Tools for Weight Loss in Overweight and Obese Young Adults (Project SMART): a 2 Year, Parallel-Group, Randomised, Controlled Trial Background
    Few weight loss interventions are evaluated for longer than a year, and even fewer employ social and mobile technologies commonly used among young adults. We assessed the efficacy of a 2 year, theory-based, weight loss intervention that was remotely and adaptively delivered via integrated user experiences with Facebook, mobile apps, text messaging, emails, a website, and technology-mediated communication with a health coach (the SMART intervention).
    
    Methods
    In this parallel-group, randomised, controlled trial, we enrolled overweight or obese college students (aged 18-35 years) from three universities in San Diego, CA, USA. Participants were randomly assigned (1:1) to receive either the intervention (SMART intervention group) or general information about health and wellness (control group). We used computer-based permuted-block randomisation with block sizes of four, stratified by sex, ethnicity, and college. Participants, study staff, and investigators were masked until the intervention was assigned. The primary outcome was objectively measured weight in kg at 24 months. Differences between groups were evaluated using linear mixed-effects regression within an intention-to-treat framework. Objectively measured weight at 6, 12, and 18 months was included as a secondary outcome. The trial is registered with ClinicalTrials.gov, number NCT01200459.
    
    Findings
    Between May 18, 2011, and May 17, 2012, 404 individuals were randomly assigned to the intervention (n=202) or control (n=202). Participants' mean (SD) age was 22.7 (3.8) years. 284 (70%) participants were female and 125 (31%) were Hispanic. Mean (SD) body-mass index at baseline was 29.0 (2.8) kg/m2. At 24 months, weight was assessed in 341 (84%) participants, but all 404 were included in analyses. Weight, adjusted for sex, ethnicity, and college, was not significantly different between the groups at 24 months (-0.79 kg [95% CI -2.02 to 0.43], p=0.204). However, weight was significantly less in the intervention group compared with the control group at 6 months (-1.33 kg [95% CI -2.36 to -0.30], p=0.011) and 12 months (-1.33 kg [-2.30 to -0.35], p=0.008), but not 18 months (-0.67 kg [95% CI -1.69 to 0.35], p=0.200). One serious adverse event in the intervention group (gallstones) could be attributable to rapid and excessive weight loss.
    
    Interpretation
    Social and mobile technologies did not facilitate sustained reductions in weight among young adults, although these approaches might facilitate limited short-term weight loss.

    Job Godino, Gina Merchant, Gregory J. Norman, Michael C. Donohue, Simon J. Marshall, James H. Fowler, Karen J. Calfas, Jeannie S. Huang, Cheryl L. Rock, William G. Griswold, Anjali Gupta, Fredric Raab, B. J. Fogg, Thomas N. Robinson, Kevin Patrick
    Lancet Diabetes and Endocrinology 4 (9): 747–755 (September 2016)
    • Commentary by Brie Turner-McGrievy

22. Social Connectedness is Associated with Fibrinogen Level in a Human Social Network Socially isolated individuals face elevated rates of illness and death. Conventional measures of social connectedness reflect an individual's perceived network and can be subject to bias and variation in reporting. In this study of a large human social network, we find that greater indegree, a sociocentric measure of friendship and familial ties identified by a subject's social connections rather than by the subject, predicts significantly lower concentrations of fibrinogen (a biomarker of inflammation and cardiac risk), after adjusting for demographics, education, medical history and known predictors of cardiac risk. The association between fibrinogen and social isolation, as measured by low indegree, is comparable to the effect of smoking, and greater than that of low education, a conventional measure of socioeconomic disadvantage. By contrast, outdegree, which reflects an individual's perceived connectedness, displays a significantly weaker association with fibrinogen concentrations.

    David A. Kim, Emelia J. Benjamin, James H. Fowler, Nicholas A. Christakis
    Proceedings of the Royal Society B 283 (1837): 20160958 (31 August 2016)
    • Supplementary Appendix
    • The Telegraph

23. Big Data Sensors of Organic Advocacy: The Case of Leonardo DiCaprio and Climate Change The strategies that experts have used to share information about social causes have historically been top-down, meaning the most influential messages are believed to come from planned events and campaigns. However, more people are independently engaging with social causes today than ever before, in part because online platforms allow them to instantaneously seek, create, and share information. In some cases this "organic advocacy" may rival or even eclipse top-down strategies. Big data analytics make it possible to rapidly detect public engagement with social causes by analyzing the same platforms from which organic advocacy spreads. To demonstrate this claim we evaluated how Leonardo DiCaprio's 2016 Oscar acceptance speech citing climate change motivated global English language news (Bloomberg Terminal news archives), social media (Twitter postings) and information seeking (Google searches) about climate change. Despite an insignificant increase in traditional news coverage (54%; 95%CI: -144 to 247), tweets including the terms “climate change” or “global warming” reached record highs, increasing 636% (95%CI: 573-699) with more than 250,000 tweets the day DiCaprio spoke. In practical terms the "DiCaprio effect" surpassed the daily average effect of the 2015 Conference of the Parties (COP) and the Earth Day effect by a factor of 3.2 and 5.3, respectively. At the same time, Google searches for "climate change" or "global warming" increased 261% (95%CI, 186-335) and 210% (95%CI 149-272) the day DiCaprio spoke and remained higher for 4 more days, representing 104,190 and 216,490 searches. This increase was 3.8 and 4.3 times larger than the increases observed during COP's daily average or on Earth Day. Searches were closely linked to content from Dicaprio's speech (e.g., "hottest year"), as unmentioned content did not have search increases (e.g., "electric car"). Because these data are freely available in real time our analytical strategy provides substantial lead time for experts to detect and participate in organic advocacy while an issue is salient. Our study demonstrates new opportunities to detect and aid agents of change and advances our understanding of communication in the 21st century media landscape.

    Eric C. Leas, Benjamin M. Althouse, Mark Dredze, Nick Obradovich, James H. Fowler, Seth M. Noar, Jon-Patrick Allem, John W. Ayers
    PLOS ONE 11 (8): e0159885 (2 August 2016)
    • Washington Post

24. From Posting to Voting: The Effects of Political Competition on Online Political Engagement How does living in a battleground state during a presidential election affect an individual's political engagement? We utilize a unique collection of 113 million Facebook status updates to compare users' political discussion during the 2008 election. "Battleground" state users are significantly more likely to discuss politics in the campaign season than are users in uncompetitive "blackout" states. Posting a political status update—a form of day-to-day engagement with politics—mediates about 20 percent of the relationship between exposure to political competition and self-reported voter turnout. This paper is among the first to use a massive quantity of social media data to explain the microfoundations of how people think, feel, and act on a daily basis in response to their political environment.

    Jaime E. Settle, Robert M. Bond, Lorenzo Coviello, Christopher J. Fariss, James H. Fowler, Jason J. Jones,
    Political Science Research and Methods 4 (2): 361–378 (May 2016)
    • Supplementary Appendix

25. Rapid Assessment of Disaster Damage Using Social Media Activity Could social media data aid in disaster response and damage assessment? Countries face both an increasing frequency and intensity of natural disasters due to climate change. And during such events, citizens are turning to social media platforms for disaster-related communication and information. Social media improves situational awareness, facilitates dissemination of emergency information, enables early warning systems, and helps coordinate relief efforts. Additionally, spatiotemporal distribution of disaster-related messages helps with real-time monitoring and assessment of the disaster itself. Here we present a multiscale analysis of Twitter activity before, during, and after Hurricane Sandy. We examine the online response of 50 metropolitan areas of the United States and find a strong relationship between proximity to Sandy's path and hurricane-related social media activity. We show that real and perceived threats -- together with the physical disaster effects -- are directly observable through the intensity and composition of Twitter's message stream. We demonstrate that per-capita Twitter activity strongly correlates with the per-capita economic damage inflicted by the hurricane. Our findings suggest that massive online social networks can be used for rapid assessment ("nowcasting") of damage caused by a large-scale disaster.

    Yury Kryvasheyeu, Haohui Chen, Nick Obradovich, Esteban Moro, Pascal Van Hentenryck, James Fowler, Manuel Cebrian
    Science Advances 2 (3): e1500779 (11 March 2016)
    • Wall Street Journal
    • Washington Post

26. Intimate Partner Violence Norms Cluster Within Households: An Observational Social Network Study in Rural Honduras Background
    Intimate partner violence (IPV) is a complex global problem, not only because it is a human rights issue, but also because it is associated with chronic mental and physical illnesses as well as acute health outcomes related to injuries for women and their children. Attitudes, beliefs, and norms regarding IPV are significantly associated with the likelihood of both IPV experience and perpetration.
    
    Methods
    We investigated whether IPV acceptance is correlated across socially connected individuals, whether these correlations differ across types of relationships, and whether social position is associated with the likelihood of accepting IPV. We used sociocentric network data from 831 individuals in rural Honduras to assess the association of IPV acceptance between socially connected individuals across 15 different types of relationships, both within and between households. We also investigated the association between network position and IPV acceptance.
    
    Results
    We found that having a social contact that accepts IPV is strongly associated with IPV acceptance among individuals. For women the clustering of IPV acceptance was not significant in between-household relationships, but was concentrated within households. For men, however, while IPV acceptance was strongly clustered within households, men's acceptance of IPV was also correlated with people with whom they regularly converse, their mothers and their siblings, regardless of household. We also found that IPV was more likely to be accepted by less socially-central individuals, and that the correlation between a social contact's IPV acceptance was stronger on the periphery, suggesting that, as a norm, it is held on the periphery of the community.
    
    Conclusion
    Our results show that differential targeting of individuals and relationships in order to reduce the acceptability and, subsequently, the prevalence of IPV may be most effective. Because IPV norms seem to be strongly held within households, the household is probably the most logical unit to target in order to implement change. This approach would include the possible benefit of a generational effect. Finally, in social contexts in which perpetration of IPV is not socially acceptable, the most effective strategy may be to implement change not at the center but at the periphery of the community.

    Holly B. Shakya, D. Alex Hughes, Derek Stafford, Nicholas A. Christakis, James H. Fowler, Jay G. Silverman
    BMC Public Health 16: 233 (8 March 2016)

27. Self-Comparisons as Motivators for Healthy Behavior Objective
    We explored whether individuals' comparison of themselves to their social contacts, specifically feeling fitter or thinner than friends, is a significant predictor of three weight-loss behaviors (dieting, reducing alcohol, exercising).
    
    Methods
    We used a longitudinal survey of a national sample of Americans (N = 20,373) to measure respondents' personal social networks and their self-comparisons to their social contacts at two annual waves.
    
    Results
    Participants who felt thinner than friends in Wave 1 had 1.16 lower odds of dieting in Wave 2. Those who felt fitter than friends in Wave 1 had 1.10 times higher odds of reducing alcohol and 1.18 times higher odds of exercising in Wave 2. We found that 20% of the relationship between feeling thin at baseline and subsequent dieting may be because feeling heavier than friends makes one want to lose weight. This same dynamic accounts for 25% of the relationship between feeling fit and dieting and 12% of the relationship between feeling thin and reducing alcohol.
    
    Conclusions
    These results suggest that normative self-comparison with important others is a potentially salient determinant of obesity-related health behavior and appears to work differently depending upon the behavior. Interventions may benefit from exploiting social comparisons in targeted ways.

    Holly B. Shakya, Nicholas A. Christakis, James H. Fowler
    Obesity 23 (12): 2477–2484 (December 2015)
    • Supplementary Appendix
    • Commentary by David Shoham

28. Linking Genes and Political Orientations: Testing the Cognitive Ability as Mediator Hypothesis Recent research has demonstrated that genetic differences explain a sizeable fraction of the variance in political orientations, but little is known about the pathways through which genes might affect political preferences. In this article, we use a uniquely assembled dataset of almost 1,000 Swedish male twin pairs containing detailed information on cognitive ability and political attitudes in order to further examine the genetic and environmental causes of political orientations. Our study makes three distinct contributions to our understanding of the etiology of political orientations: (1) we report heritability estimates across different dimensions of political ideology; (2) we show that cognitive ability and political orientations are related; and (3) we provide evidence consistent with the hypothesis that cognitive ability mediates part of the genetic influence on political orientations. These findings provide important clues about the nature of the complex pathways from molecular genetic variation to political orientations.

    Sven Oskarsson, David Cesarini, Christopher T. Dawes, James H. Fowler, Magnus Johannesson, Patrik K. E. Magnusson, Jan Teorell
    Political Psychology 36 (6): 649–665 (December 2015)
    • Online Appendix

29. Online Social Networks and Offline Protest Large-scale protests occur frequently and sometimes overthrow entire political systems. Meanwhile, online social networks have become an increasingly common component of people's lives. We present a large-scale longitudinal study that connects online social media behaviors to offline protest. Using almost 14 million geolocated tweets and data on protests from 16 countries during the Arab Spring, we show that increased coordination of messages on Twitter using specific hashtags is associated with increased protests the following day. The results also show that traditional actors like the media and elites are not driving the results. These results indicate social media activity correlates with subsequent large-scale decentralized coordination of protests, with important implications for the future balance of power between citizens and their states.

    Zachary C. Steinert-Threlkeld, Delia Mocanu, Alessandro Vespignani, James H. Fowler
    EPJ Data Science 4 (19): 1–9 (November 2015)

30. Social Network Targeting to Maximise Population Behaviour Change: A Cluster Randomised Controlled Trial Background
    Information and behaviour can spread through interpersonal ties. By targeting influential individuals, health interventions that harness the distributive properties of social networks could be made more effective and efficient than those that do not. Our aim was to assess which targeting methods produce the greatest cascades or spillover effects and hence maximise population-level behaviour change.
    
    Methods
    In this cluster randomised trial, participants were recruited from villages of the Department of Lempira, Honduras. We blocked villages on the basis of network size, socioeconomic status, and baseline rates of water purification, for delivery of two public health interventions: chlorine for water purification and multivitamins for micronutrient deficiencies. We then randomised villages, separately for each intervention, to one of three targeting methods, introducing the interventions to 5% samples composed of either: randomly selected villagers (n=9 villages for each intervention); villagers with the most social ties (n=9); or nominated friends of random villagers (n=9; the last strategy exploiting the so-called friendship paradox of social networks). Participants and data collectors were not aware of the targeting methods. Primary endpoints were the proportions of available products redeemed by the entire population under each targeting method. This trial is registered with ClinicalTrials.gov, number NCT01672580.
    
    Findings
    Between Aug 4, and Aug 14, 2012, 32 villages in rural Honduras (25-541 participants each; total study population of 5773) received public health interventions. For each intervention, nine villages (each with 1-20 initial target individuals) were randomised, using a blocked design, to each of the three targeting methods. In nomination-targeted villages, 951 (74.3%) of 1280 available multivitamin tickets were redeemed compared with 940 (66.2%) of 1420 in randomly targeted villages and 744 (61.0%) of 1220 in indegree-targeted villages. All pairwise differences in redemption rates were significant (p<0.01) after correction for multiple comparisons. Targeting nominated friends increased adoption of the nutritional intervention by 12.2% compared with random targeting (95% CI 6.9-17.9). Targeting the most highly connected individuals, by contrast, produced no greater adoption of either intervention, compared with random targeting.
    
    Interpretation
    Introduction of a health intervention to the nominated friends of random individuals can enhance that intervention's diffusion by exploiting intrinsic properties of human social networks. This method has the additional advantage of scalability because it can be implemented without mapping the network. Deployment of certain types of health interventions via network targeting, without increasing the number of individuals targeted or the resources used, could enhance the adoption and efficiency of those interventions, thereby improving population health.
    
    Funding
    National Institutes of Health, The Bill and Melinda Gates Foundation, Star Family Foundation, and the Canadian Institutes of Health Research.

    David A. Kim, Alison R. Hwong, Derek Stafford, D. Alex Hughes, A. James O'Malley, James H. Fowler, Nicholas A. Christakis
    The Lancet 386 (9989): 145–153 (11–17 July 2015)
    • Supplementary Appendix
    • Commentary by Felix Elwert
    • Boston Globe

31. Clinical Trial Management of Participant Recruitment, Enrollment, Engagement, and Retention in the SMART Study Using a Marketing and Information Technology (MARKIT) Model Advances in information technology and near ubiquity of the Internet have spawned novel modes of communication and unprecedented insights into human behavior via the digital footprint. Health behavior randomized controlled trials (RCTs), especially technology-based, can leverage these advances to improve the overall clinical trials management process and benefit from improvements at every stage, from recruitment and enrollment to engagement and retention. In this paper, we report the results for recruitment and retention of participants in the SMART study and introduce a new model for clinical trials management that is a result of interdisciplinary team science. The MARKIT model brings together best practices from information technology, marketing, and clinical research into a single framework to maximize efforts for recruitment, enrollment, engagement, and retention of participants into a RCT. These practices may have contributed to the study's on-time recruitment that was within budget, 86% retention at 24 months, and a minimum of 57% engagement with the intervention over the 2-year RCT. Use of technology in combination with marketing practices may enable investigators to reach a larger and more diverse community of participants to take part in technology-based clinical trials, help maximize limited resources, and lead to more cost-effective and efficient clinical trial management of study participants as modes of communication evolve among the target population of participants.

    Anjali Gupta, Karen J. Calfas, Simon J. Marshall, Thomas N. Robinson, Cheryl L. Rock, Jeannie S. Huang, Melanie Epstein-Corbin, Christina Servetas, Michael C. Donohue, Gregory J. Norman, Fredric Raab, Gina Merchant, James H. Fowler, William G. Griswold, B. J. Fogg, Kevin Patrick
    Contemporary Clinical Trials 42 (1): 185–195 (May 2015)

32. Social Network Predictors of Latrine Ownership Poor sanitation, including the lack of clean functioning toilets, is a major factor contributing to morbidity and mortality from infectious diseases in the developing world. We examine correlates of latrine ownership in rural India with a focus on social network predictors. Participants from 75 villages provided the names of their social contacts as well as their own relevant demographic and household characteristics. Using these measures, we test whether the latrine ownership of an individual's social contacts is a significant predictor of individual latrine ownership. We also investigate whether network centrality significantly predicts latrine ownership, and if so, whether it moderates the relationship between the latrine ownership of the individual and that of her social contacts. Our results show that, controlling for the standard predictors of latrine ownership such as caste, education, and income, individuals are more likely to own latrines if their social contacts own latrines. Interaction models suggest that this relationship is stronger among those of the same caste, the same education, and those with stronger social ties. We also find that more central individuals are more likely to own latrines, but the correlation in latrine ownership between social contacts is strongest among individuals on the periphery of the network. Although more data is needed to determine how much the clustering of latrine ownership may be caused by social influence, the results here suggest that interventions designed to promote latrine ownership should consider focusing on those at the periphery of the network. The reason is that they are 1) less likely to own latrines and 2) more likely to exhibit the same behavior as their social contacts, possibly as a result of the spread of latrine adoption from one person to another.

    Holly B. Shakya, Nicholas A. Christakis, James H. Fowler
    Social Science & Medicine 125: 129–138 (January 2015)
    • Supplementary Information

33. The Role of Self-Interest in Elite Bargaining One of the best-known and most replicated laboratory results in behavioral economics is that bargainers frequently reject low offers, even when it harms their material self-interest. This finding could have important implications for international negotiations on many problems facing humanity today, because models of international bargaining assume exactly the opposite: that policy makers are rational and self-interested. However, it is unknown whether elites who engage in diplomatic bargaining will similarly reject low offers because past research has been based almost exclusively on convenience samples of undergraduates, members of the general public, or small-scale societies rather than highly experienced elites who design and bargain over policy. Using a unique sample of 102 policy and business elites who have an average of 21 y of practical experience conducting international diplomacy or policy strategy, we show that, compared with undergraduates and the general public, elites are actually more likely to reject low offers when playing a standard “ultimatum game” that assesses how players bargain over a fixed resource. Elites with more experience tend to make even higher demands, suggesting that this tendency only increases as policy makers advance to leadership positions. This result contradicts assumptions of rational self-interested behavior that are standard in models of international bargaining, and it suggests that the adoption of global agreements on international trade, climate change, and other important problems will not depend solely on the interests of individual countries, but also on whether these accords are seen as equitable to all member states.

    Brad L. LeVeck, D. Alex Hughes, James H. Fowler, Emilie M. Hafner-Burton, David G. Victor
    PNAS 111 (52): 18536–18541 (30 December 2014)
    • Supplementary Information
    • Bloomberg

34. Static Network Structure Can Stabilize Human Cooperation The evolution of cooperation in network-structured populations has been a major focus of theoretical work in recent years. When players are embedded in fixed networks, cooperators are more likely to interact with, and benefit from, other cooperators. In theory, this clustering can foster cooperation on fixed networks under certain circumstances. Laboratory experiments with humans, however, have thus far found no evidence that fixed network structure actually promotes cooperation. Here, we provide such evidence and help to explain why others failed to find it. First, we show that static networks can lead to a stable high level of cooperation, outperforming well-mixed populations. We then systematically vary the benefit that cooperating provides to one's neighbors relative to the cost required to cooperate (b/c), as well as the average number of neighbors in the network (k). When b/c > k, we observe high and stable levels of cooperation. Conversely, when b/c ≤ k or players are randomly shuffled, cooperation decays. Our results are consistent with a quantitative evolutionary game theoretic prediction for when cooperation should succeed on networks and, for the first time to our knowledge, provide an experimental demonstration of the power of static network structure for stabilizing human cooperation.

    David G. Rand, Martin A. Nowak, James H. Fowler, Nicholas A. Christakis
    PNAS 111 (48): 17093–17098 (2 December 2014)
    • Supplementary Information

35. Words on the Web: Noninvasive Detection of Emotional Contagion in Online Social Networks Does semantic expression spread online from person to person? And if so, what kinds of expression are most likely to spread? To address these questions, we developed a nonexperimental, noninvasive method to detect and quantify contagion of semantic expression in massive online social networks, which we review and discuss here. Using only observational data, the method avoids performing emotional experiments on users of online social networks, a research practice that recently became an object of criticism and concern. Our model combines geographic aggregation and instrumental variables regression to measure the effect of an exogenous variable on an individual's expression and the influence of this change on the expression of others to whom that individual is socially connected. In a previous work, we applied our method to the emotional content of posts generated by a large sample of users over a period of three years. Those results suggest that each post expressing a positive or negative emotion can cause friends to generate one to two additional posts expressing the same emotion, and it also inhibits their use of the opposite emotion. Here, we generalize our method so it can be applied to contexts different than emotional expression and to different forms of content generated by the users of online platforms. The method allows us to determine the usage of words in the same semantic category spread, and to estimate a signed relationship between different semantic categories, showing that an increase in the usage of one category alters the usage of another category in one's social contacts. Finally, it also allows us to estimate the total cumulative effect that a person has on all of her social contacts.

    Lorenzo Coviello, James H. Fowler, Massimo Franceschetti
    Proceedings of the IEEE 102 (12): 1911–1921 (December 2014)

36. Credit Card Borrowing and the Monoamine Oxidase A (MAOA) Gene Using a discovery and replication sample from a U.S. representative data set, we show that a functional polymorphism on the MAOA gene is associated with credit card borrowing behavior. For the combined sample of approximately 12,000 individuals we find that having one or both MAOA alleles of the less transcriptionally efficient type raises the average likelihood of reporting credit card debt by about 4%. These results suggest that behavioral models benefit from integrating genetic variation and that economists should consider the welfare consequences of possible discrimination by lenders on the basis of genotype.

    Jan-Emmanuel De Neve, James H. Fowler
    Journal of Economic Behavior and Organization 107 (Part B): 428–439 (November 2014)
    • Newsweek

37. The Relationship Between Genes, Psychological Traits, and Political Participation Recent research demonstrates that a wide range of political attitudes, beliefs, and behaviors can be explained in part by genetic variation. However, these studies have not yet identified the mechanisms that generate such a relationship. Some scholars have speculated that psychological traits mediate the relationship between genes and political participation, but so far there have been no empirical tests. Here we focus on the role of three psychological traits that are believed to influence political participation: cognitive ability, personal control, and extraversion. Utilizing a unique sample of more than 2,000 Swedish twin pairs, we show that a common genetic factor can explain most of the relationship between these psychological traits and acts of political participation as well as predispositions related to participation. While our analysis is not a definitive test, our results suggest an upper bound for a proposed mediation relationship between genes, psychological traits, and political participation.

    Christopher T. Dawes, David Cesarini, James H. Fowler, Magnus Johannesson, Patrik K. E. Magnusson, Sven Oskarsson
    American Journal of Political Science 58 (4): 888–903 (October 2014)

38. Decision Maker Preferences for International Legal Cooperation What determines preferences for cooperation through international legal agreements? Why do some decision makers prefer big multilateral agreements while others prefer cooperation in small clubs? Does enforcement encourage or deter institutional cooperation? We use experiments drawn from behavioral economics and cognitive psychology—along with a substantive survey focused on international trade—to illustrate how two behavioral traits (patience and strategic reasoning) of the individual people asked to play key roles in negotiating and ratifying an international treaty shape their preferences for how treaties are designed and whether they are ratified. Patient subjects were more likely to prefer treaties with larger numbers of countries (and larger long-term benefits), as were subjects with the skill to anticipate how others will respond over multiple iterations of strategic games. The presence of an enforcement mechanism increased subjects' willingness to ratify treaties; however, the effect of strategic reasoning was double the effect of adding enforcement to a trade agreement: more strategic subjects were particularly likely to favor ratifying the agreement. We report these results for a sample of 509 university students and also show how similar patterns are revealed in a unique sample of 92 actual U.S. policy elites, suggesting that under some conditions certain types of university student convenience samples can be useful for revealing elite-dominated policy preferences. The implication is that different types of people in the same situation may prefer to approach decision making tasks and reason through trade offs in materially different ways.

    Emilie M. Hafner-Burton, Brad L. LeVeck, David G. Victor, James H. Fowler
    International Organization 68 (4): 845–876 (September 2014)
    • Washington Post

39. Friendship and Natural Selection More than any other species, humans form social ties to individuals who are neither kin nor mates, and these ties tend to be with similar people. Here, we show that this similarity extends to genotypes. Across the whole genome, friends' genotypes at the single nucleotide polymorphism level tend to be positively correlated (homophilic). In fact, the increase in similarity relative to strangers is at the level of fourth cousins. However, certain genotypes are also negatively correlated (heterophilic) in friends. And the degree of correlation in genotypes can be used to create a "friendship score" that predicts the existence of friendship ties in a hold-out sample. A focused gene set analysis indicates that some of the overall correlation in genotypes can be explained by specific systems; for example, an olfactory gene set is homophilic and an immune system gene set is heterophilic, suggesting that these systems may play a role in the formation or maintenance of friendship ties and that friends may be a kind of "functional kin." Finally, homophilic genotypes exhibit significantly higher measures of positive selection, suggesting that, on average, they may yield a synergistic fitness advantage that has been helping to drive recent human evolution.

    Nicholas A. Christakis, James H. Fowler
    PNAS 111 (Supplement 3): 10796–10801 (22 July 2014)
    • Supplementary Information
    • Washington Post
    • NPR
    • CNN
    • USA Today
    • UCSD Press Release

40. Evolutionary Origins of the Endowment Effect: Evidence from Hunter-Gatherers The endowment effect, the tendency to value possessions more than non-possessions, is a well known departure from rational choice, surviving replication in numerous settings. This paper investigates the universality of the endowment effect, as well as its evolutionary significance and dependence on environmental factors. To this end, we experimentally test for the endowment effect in an isolated and evolutionarily relevant population of hunter-gatherers; the Hadza Bushmen of Northern Tanzania. We find that Hadza living in isolated regions do not display the endowment effect, while Hadza living in a geographic region with increased exposure to modern society and markets, do display the endowment effect.

    Coren L. Apicella, Eduardo M. Azevedo, James H. Fowler, Nicholas A. Christakis
    American Economic Review 104 (6): 1793–1805 (June 2014)
    • NPR
    • U Penn Press Release

41. Click 'Like' to Change Your Behavior: A Mixed Methods Study of College Students' Exposure to and Engagement with Facebook Content Designed for Weight-Loss Background
    Overweight or obesity is prevalent among college students and many gain weight during this time. Traditional face-to-face weight loss interventions have not worked well in this population. Facebook is an attractive tool for delivering weight loss interventions for college students because of its popularity, potential to deliver strategies found in successful weight loss interventions, and ability to support ongoing adaptation of intervention content.
    
    Objective
    The objective of this study was to describe participant exposure to a Facebook page designed to deliver content to overweight/obese college students in a weight loss randomized controlled trial (N=404) and examine participant engagement with behavior change campaigns for weight loss delivered via Facebook.
    
    Methods
    The basis of the intervention campaign model were 5 self-regulatory techniques: intention formation, action planning, feedback, goal review, and self-monitoring. Participants were encouraged to engage their existing social network to meet their weight loss goals. A health coach moderated the page and modified content based on usage patterns and user feedback. Quantitative analyses were conducted at the Facebook post- and participant-level of analysis. Participant engagement was quantified by Facebook post type (eg, status update) and interaction (eg, like) and stratified by weight loss campaign (sequenced vs nonsequenced). A subset of participants were interviewed to evaluate the presence of passive online engagement or "lurking."
    
    Results
    The health coach posted 1816 unique messages to the study's Facebook page over 21 months, averaging 3.45 posts per day (SD 1.96, range 1-13). In all, 72.96% (1325/1816) of the posts were interacted with at least once (eg, liked). Of these, approximately 24.75% (328/1325) had 1-2 interactions, 23.39% (310/1325) had 3-5 interactions, 25.13% (333/1325) had 6-8 interactions, and 41 posts had 20 or more interactions (3.09%, 41/1325). There was significant variability among quantifiable (ie, visible) engagement. Of 199 participants in the final intervention sample, 32 (16.1%) were highly active users and 62 (31.2%) never visibly engaged with the intervention on Facebook. Polls were the most popular type of post followed by photos, with 97.5% (79/81) and 80.3% (386/481) interacted with at least once. Participants visibly engaged less with posts over time (partial r = -.33; P<.001). Approximately 40% of the participants interviewed (12/29, 41%) reported passively engaging with the Facebook posts by reading but not visibly interacting with them.
    
    Conclusions
    Facebook can be used to remotely deliver weight loss intervention content to college students with the help of a health coach who can iteratively tailor content and interact with participants. However, visible engagement with the study's Facebook page was highly variable and declined over time. Whether the level of observed engagement is meaningful in terms of influencing changes in weight behaviors and outcomes will be evaluated at the completion of the overall study.

    Gina Merchant, Nadir Weibel, Kevin Patrick, James H. Fowler, Gregory J. Norman, Anjali Gupta, Christina Servetas, Karen J. Calfas, Ketaki Raste, Laura Pina, Michael C. Donohue, Simon J. Marshall
    Journal of Medical Internet Research 16 (6): e158 (June 2014)

42. Association Between Social Network Communities and Health Behavior: An Observational Sociocentric Network Study of Latrine Ownership in Rural India Objectives
    We identified communities of interconnected people that might serve as normative reference groups for individual-level behavior related to latrine adoption.
    
    Methods
    We applied an algorithmic social network method to determine the network community from respondent-reported social ties of 16,403 individuals in 75 villages in rural Karnataka, India; data were collected from 2006 to 2008. We used multilevel modeling to test the association between latrine ownership and community-level and village-level latrine ownership. We also investigated the degree to which network cohesion affected individual latrine ownership.
    
    Results
    Three levels of social contacts (direct friends, social network community, and village) significantly predicted individual latrine ownership, but the strongest effect was found at the level of social network communities. In communities with high levels of network cohesion, the likelihood was decreased that any individual would own a latrine; this effect was significant only at lower levels of latrine ownership, suggesting a role for network cohesion in facilitating the nonownership norm.
    
    Conclusions
    Although many international health and development interventions target village units, these results raise the possibility that the optimal target for public health interventions may not be determined through geography but through social network interactions.

    Holly B. Shakya, Nicholas A. Christakis, James H. Fowler
    American Journal of Public Health 104 (5): 930–937 (May 2014)

43. Using Friends as Sensors to Detect Global-Scale Contagious Outbreaks Recent research has focused on the monitoring of global-scale online data for improved detection of epidemics, mood patterns, movements in the stock market political revolutions, box-office revenues, consumer behaviour and many other important phenomena. However, privacy considerations and the sheer scale of data available online are quickly making global monitoring infeasible, and existing methods do not take full advantage of local network structure to identify key nodes for monitoring. Here, we develop a model of the contagious spread of information in a global-scale, publicly-articulated social network and show that a simple method can yield not just early detection, but advance warning of contagious outbreaks. In this method, we randomly choose a small fraction of nodes in the network and then we randomly choose a friend of each node to include in a group for local monitoring. Using six months of data from most of the full Twittersphere, we show that this friend group is more central in the network and it helps us to detect viral outbreaks of the use of novel hashtags about 7 days earlier than we could with an equal-sized randomly chosen group. Moreover, the method actually works better than expected due to network structure alone because highly central actors are both more active and exhibit increased diversity in the information they transmit to others. These results suggest that local monitoring is not just more efficient, but also more effective, and it may be applied to monitor contagious processes in global-scale networks.

    Manuel Garcia-Herranz, Esteban Moro, Manuel Cebrian, Nicholas A. Christakis, James H. Fowler
    PLOS ONE 9 (4): e92413 (9 April 2014)
    • Supplementary Information
    • Tech Review

44. Corruption Drives the Emergence of Civil Society Centralized sanctioning institutions have been shown to emerge naturally through social learning, displace all other forms of punishment and lead to stable cooperation. However, this result provokes a number of questions. If centralized sanctioning is so successful, then why do many highly authoritarian states suffer from low levels of cooperation? Why do states with high levels of public good provision tend to rely more on citizen-driven peer punishment? Here, we consider how corruption influences the evolution of cooperation and punishment. Our model shows that the effectiveness of centralized punishment in promoting cooperation breaks down when some actors in the model are allowed to bribe centralized authorities. Counterintuitively, a weaker centralized authority is actually more effective because it allows peer punishment to restore cooperation in the presence of corruption. Our results provide an evolutionary rationale for why public goods provision rarely flourishes in polities that rely only on strong centralized institutions. Instead, cooperation requires both decentralized and centralized enforcement. These results help to explain why citizen participation is a fundamental necessity for policing the commons.

    Sherief Abdallah, Rasha Sayed, Iyad Rahwan, Brad L. LeVeck, Manuel Cebrian, Alex Rutherford, James H. Fowler
    Journal of the Royal Society Interface 11 (93): 2013044 (6 April 2014)
    • Supplementary Information

45. Relationships Between Depression, Gender, and Unhealthy Weight Loss Practices Among Overweight or Obese College Students Introduction
    Unhealthy weight loss practices are common among female college students. It is unknown if these practices are also most common among women in the subset of overweight or obese college students or if these practices are related to depression. We examined the relationship between gender, depression, and unhealthy weight loss practices among overweight or obese college students.
    
    Methods
    Students (body mass index between 25.0 and 34.9 kg/m2) from three Southern California universities (Mage = 22 years, SD = 4; 70% women) were recruited from May 2011 to May 2012 for participation in a weight loss clinical trial (N = 404). Logistic regressions were performed with baseline data to assess the cross-sectional relationship between self-reported unhealthy weight loss practices and gender and depression as measured by the Center for Epidemiologic Studies Depression short form.
    
    Results
    Twenty-nine percent of participants reported engaging in at least one unhealthy weight loss behavior (e.g., fasting, purging) over the last 30 days, with no differences by gender. Self-report of at least one unhealthy weight loss behavior was associated with report of symptoms of depression (eB = 1.14 [confidence interval, CI: 1.08-1.20]), adjusting for potential confounders. Interactions between gender and depression were not significant (eB = 1.04 [CI: 0.93-1.16]).
    
    Conclusion
    Among an overweight or obese sample of college students, unhealthy weight loss practices were equally common in both genders, and students with depressive symptomatology were at greatest risk. Obesity interventions targeting overweight or obese college students should educate both men and women about the dangers of unhealthy weight loss practices. In addition, screening for depression can help identify students who would benefit from additional supportive and coping strategies and resources.

    Evelyn P. Davila, Julia K. Kolodziejczyk, Gregory J. Norman, Karen J. Calfas, Jeannie S. Huang, Cheryl L. Rock, William G. Griswold, James H. Fowler, Simon J. Marshall, Anjali Gupta, Kevin Patrick
    Eating Behaviors 15 (2): 271–274 (April 2014)

46. Detecting Emotional Contagion in Massive Social Networks Happiness and other emotions spread between people in direct contact, but it is unclear whether massive online social networks also contribute to this spread. Here, we elaborate a novel method for measuring the contagion of emotional expression. With data from millions of Facebook users, we show that rainfall directly influences the emotional content of their status messages, and it also affects the status messages of friends in other cities who are not experiencing rainfall. For every one person affected directly, rainfall alters the emotional expression of about one to two other people, suggesting that online social networks may magnify the intensity of global emotional synchrony.

    Lorenzo Coviello, Yunkyu Sohn, Adam D. I. Kramer, Cameron Marlow, Massimo Franceschetti, Nicholas A. Christakis, James H. Fowler
    PLOS ONE 9 (3): e90315 (12 March 2014)
    • Supplementary Information
    • Time
    • Wall Street Journal
    • USA Today
    • NPR
    • UCSD Press Release

47. Same-Sex Sexual Attraction Does Not Spread in Adolescent Social Networks Peers have a powerful effect on adolescents' beliefs, attitudes, and behaviors. Here, we examine the role of social networks in the spread of attitudes towards sexuality using data from the National Longitudinal Study of Adolescent Health (Add Health). Although we found evidence that both sexual activity (OR = 1.79) and desire to have a romantic relationship (OR = 2.69) may spread from person to person, attraction to same sex partners did not spread (OR = 0.96). Analyses of comparable power to those that suggest positive and significant peer-to-peer influence in sexual behavior fail to demonstrate a significant relationship on sexual attraction between friends or siblings. These results suggest that peer influence has little or no effect on the tendency toward heterosexual or homosexual attraction in teens, and that sexual orientation is not transmitted via social networks.

    Tiffany A. Brakefield, Sara C. Mednick, Helen W. Wilson, Jan-Emmanuel De Neve, Nicholas A. Christakis, James H. Fowler
    Archives of Sexual Behavior 43 (2): 335–344 (February 2014)
    • Discover Magazine

48. Core-Periphery Structure in Networks Intermediate-scale (or "meso-scale") structures in networks have received considerable attention, as the algorithmic detection of such structures makes it possible to discover network features that are not apparent either at the local scale of nodes and edges or at the global scale of summary statistics. Numerous types of meso-scale structures can occur in networks, but investigations of such features have focused predominantly on the identification and study of community structure. In this paper, we develop a new method to investigate the meso-scale feature known as core-periphery structure, which entails identifying densely connected core nodes and sparsely connected peripheral nodes. In contrast to communities, the nodes in a core are also reasonably well connected to those in a network's periphery. Our new method of computing core-periphery structure can identify multiple cores in a network and takes into account different possible core structures. We illustrate the differences between our method and several existing methods for identifying which nodes belong to a core, and we use our technique to examine core-periphery structure in examples of friendship, collaboration, transportation, and voting networks.

    Puck Rombach, Mason A. Porter, James H. Fowler, Peter J. Mucha
    SIAM Journal on Applied Mathematics 74 (1): 167–190 (February 2014)

49. Prediction of Mortality Using On-Line, Self-Reported Health Data: Empirical Test of the Realage Score Objective
    We validate an online, personalized mortality risk measure called "RealAge" assigned to 30 million individuals over the past 10 years.
    
    Methods
    188,698 RealAge survey respondents were linked to California Department of Public Health death records using a one-way cryptographic hash of first name, last name, and date of birth. 1,046 were identified as deceased. We used Cox proportional hazards models and receiver operating characteristic (ROC) curves to estimate the relative scales and predictive accuracies of chronological age, the RealAge score, and the Framingham ATP-III score for hard coronary heart disease (HCHD) in this data. To address concerns about selection and to examine possible heterogeneity, we compared the results by time to death at registration, underlying cause of death, and relative health among users.
    
    Results
    The RealAge score is accurately scaled (hazard ratios: age 1.076; RealAge-age 1.084) and more accurate than chronological age (age c-statistic: 0.748; RealAge c-statistic: 0.847) in predicting mortality from hard coronary heart disease following survey completion. The score is more accurate than the Framingham ATP-III score for hard coronary heart disease (c-statistic: 0.814), perhaps because self-reported cholesterol levels are relatively uninformative in the RealAge user sample. RealAge predicts deaths from malignant neoplasms, heart disease, and external causes. The score does not predict malignant neoplasm deaths when restricted to users with no smoking history, no prior cancer diagnosis, and no indicated health interest in cancer (p-value 0.820).
    
    Conclusion
    The RealAge score is a valid measure of mortality risk in its user population.

    William R. Hobbs, James H. Fowler
    PLOS ONE 9 (1): e86385 (17 January 2014)
    • Supplementary Information

50. Widowhood Effects in Voter Participation Past research suggests that spouses influence one another to vote, but focuses almost exclusively on correlation in spousal turnout. It is therefore difficult to establish whether spouses mobilize each other or tend to marry similar others. Here, we test the spousal dependency hypothesis by examining voting behavior before and after the death of a spouse. We link nearly 6 million California voter records to Social Security death records, and use both coarsened exact matching and multiple cohort comparison to estimate the effects of spousal loss. The results show that after turnout rates stabilize, widowed individuals vote nine percentage points less than they would had their spouse still been living, and that this change may persist indefinitely. Variation in this "widower effect" on voting supports a social isolation explanation for the sudden and persistent drop in turnout. A conservative estimate of this effect nationwide accounts for one million 'lost votes' in non-presidential elections.

    William R. Hobbs, Nicholas A. Christakis, James H. Fowler
    American Journal of Political Science 58 (1): 1–16 (January 2014)
    • Supplementary Information
    • The Atlantic

51. A Natural Experiment in Proposal Power and Electoral Success Does lawmaker behavior influence electoral outcomes? Observational studies cannot elucidate the effect of legislative proposals on electoral outcomes, since effects are confounded by unobserved differences in legislative and political skill. We take advantage of a unique natural experiment in the Canadian House of Commons that allows us to estimate how proposing legislation affects election outcomes. The right of non-cabinet members to propose legislation is assigned by lottery. Comparing outcomes between those who were granted the right to propose and those who were not, we show that incumbents of the governing party enjoy a 2.7 percentage point bonus in the election following the introduction of a single piece of legislation, which translates to a 7% increase in the probability of winning. The causal effect results from more campaign donations and higher likeability amongst constituents. These results demonstrate experimentally that what politicians do as lawmakers has a causal effect on electoral outcomes.

    Peter J. Loewen, Royce Koop, Jaime E. Settle, James H. Fowler
    American Journal of Political Science 58 (1): 189–196 (January 2014)

52. Design and Implementation of a Randomized Controlled Social and Mobile Weight Loss Trial for Young Adults (Project SMART) Purpose
    To describe the theoretical rationale, intervention design, and clinical trial of a two-year weight control intervention for young adults deployed via social and mobile media.
    
    Methods
    A total of 404 overweight or obese college students from three Southern California universities (Mean age = 22 (±4) years; Mean BMI = 29 (±2.8); 70% female) were randomized to participate in the intervention or to receive an informational web-based weight loss program. The intervention is based on behavioral theory and integrates intervention elements across multiple touch points, including Facebook, text messaging, smartphone applications, blogs, and e-mail. Participants are encouraged to seek social support among their friends, self-monitor their weight weekly, post their health behaviors on Facebook, and e-mail their weight loss questions/concerns to a health coach. The intervention is adaptive because new theory-driven and iteratively tailored intervention elements are developed and released over the course of the two-year intervention in response to patterns of use and user feedback. Measures of body mass index, waist circumference, diet, physical activity, sedentary behavior, weight management practices, smoking, alcohol, sleep, body image, self-esteem, and depression occur at 6, 12, 18, and 24 months. Currently, all participants have been recruited, and all are in the final year of the trial.
    
    Conclusion:
    Theory-driven, evidence-based strategies for physical activity, sedentary behavior, and dietary intake can be embedded in an intervention using social and mobile technologies to promote healthy weight-related behaviors in young adults.

    Kevin Patrick, Simon J. Marshall, Evelyn P. Davila, Julia K. Kolodziejczyk, James H. Fowler, Karen J. Calfas, Jeannie S. Huang, Cheryl L. Rock, William G. Griswold, Anjali Gupta, Gina Merchant, Gregory J. Norman, Fredric Raab, Michael C. Donohue, B. J. Fogg, Thomas N. Robinson
    Contemporary Clinical Trials 37 (1): 10–18 (January 2014)

53. Emotion Regulation as the Foundation of Political Attitudes: Does Reappraisal Decrease Support for Conservative Policies? Cognitive scientists, behavior geneticists, and political scientists have identified several ways in which emotions influence political attitudes, and psychologists have shown that emotion regulation can have an important causal effect on physiology, cognition, and subjective experience. However, no work to date explores the possibility that emotion regulation may shape political ideology and attitudes toward policies. Here, we conduct four studies that investigate the role of a particular emotion regulation strategy —“ reappraisal in particular. Two observational studies show that individual differences in emotion regulation styles predict variation in political orientations and support for conservative policies. In the third study, we experimentally induce disgust as the target emotion to be regulated and show that use of reappraisal reduces the experience of disgust, thereby decreasing moral concerns associated with conservatism. In the final experimental study, we show that use of reappraisal successfully attenuates the relationship between trait-level disgust sensitivity and support for conservative policies. Our findings provide the first evidence of a critical link between emotion regulation and political attitudes.

    Jooa Julia Lee, Yunkyu Sohn, James H. Fowler
    PLOS ONE 8 (12): e83143 (18 December 2013)

54. Breaking Up is Hard to Do, Unless Everyone Else is Doing it Too: Social Network Effects on Divorce in a Longitudinal Sample Divorce represents the dissolution of a social tie, but it is also possible that attitudes about divorce flow across social ties. To explore how social networks influence divorce and vice versa, we exploit a longitudinal data set from the long-running Framingham Heart Study. The results suggest that divorce can spread between friends. Clusters of divorces extend to two degrees of separation in the network. Popular people are less likely to get divorced, divorcees have denser social networks, and they are much more likely to remarry other divorcees. Interestingly, the presence of children does not influence the likelihood of divorce, but each child reduces the susceptibility to being influenced by peers who get divorced. Overall, the results suggest that attending to the health of one's friends' marriages may serve to support and enhance the durability of one's own relationship, and that, from a policy perspective, divorce should be understood as a collective phenomenon that extends beyond those directly affected.

    Rose McDermott, James H. Fowler, Nicholas A. Christakis
    Social Forces 92 (2): 491–519 (December 2013)
    • Good Morning America
    • ABC World News
    • CTV
    • Pew Research Center

55. Quality Versus Quantity of Social Ties in Experimental Cooperative Networks Recent studies suggest that allowing individuals to choose their partners can help to maintain cooperation in human social networks; this behaviour can supplement behavioural reciprocity, whereby humans are influenced to cooperate by peer pressure. However, it is unknown how the rate of forming and breaking social ties affects our capacity to cooperate. Here we use a series of online experiments involving 1,529 unique participants embedded in 90 experimental networks, to show that there is a 'Goldilocks' effect of network dynamism on cooperation. When the rate of change in social ties is too low, subjects choose to have many ties, even if they attach to defectors. When the rate is too high, cooperators cannot detach from defectors as much as defectors re-attach and, hence, subjects resort to behavioural reciprocity and switch their behaviour to defection. Optimal levels of cooperation are achieved at intermediate levels of change in social ties.

    Hirokazu Shirado, Feng Fu, James H. Fowler, Nicholas A. Christakis
    Nature Communications 4: 2814 (14 November 2013)

56. The Mathematics of Murder The mass killing of 20 children and 6 adults on 14 December 2012 at Sandy Hook Elementary School in Newtown, Connecticut, has revived an enduring controversy about gun control in the United States. Gun-control advocates believe that widespread gun ownership increases the rate of gun-related crime and homicide, whereas critics argue that gun availability actually decreases gun violence because potential assailants are less likely to commit such crimes if they believe citizens are armed. But who is right? In an article published in PLOS ONE, Wodarz and Komarova describe an elegant and highly parsimonious mathematical model designed to answer exactly this question. And, in an extremely cautious way, they suggest that more guns make things worse.

    Adeline Lo, James H. Fowler
    Nature 501: 170–171 (12 September 2013)

57. The Evolution of Error Counterintuitively, biases in behavior or cognition can improve decision making. Under conditions of uncertainty and asymmetric costs of 'false-positive' and 'false-negative' errors, biases can lead to mistakes in one direction but — in so doing — steer us away from more costly mistakes in the other direction. For example, we sometimes think sticks are snakes (which is harmless), but rarely that snakes are sticks (which can be deadly). We suggest that 'error management' biases: (i) have been independently identified by multiple interdisciplinary studies, suggesting the phenomenon is robust across domains, disciplines, and methodologies; (ii) represent a general feature of life, with common sources of variation; and (iii) offer an explanation, in error manage- ment theory (EMT), for the evolution of cognitive biases as the best way to manage errors under cognitive and evolutionary constraints.

    Dominic D. P. Johnson, Daniel T. Blumenstein, James H. Fowler, Martie G. Haselton
    Trends in Ecology & Evolution 28 (8): 474–481 (August 2013)

58. Complexity and Simplicity in the Evolution of Decision-Making Biases Marshall et al. critique recent evolutionary explanations of decision-making biases, focusing on Johnson and Fowler's model of overconfidence and Trivers' model of self-deception. We agree with Marshall et al.'s central premise that a Bayesian decision-maker would also be able to optimize fitness in these settings. However, as their own argument makes clear, the point is that Bayesians require an extraordinary amount of information, as well as processing power, to achieve the same behavior.

    Dominic D. P. Johnson, James H. Fowler
    Trends in Ecology & Evolution 28 (8): 446–447 (August 2013)

59. Contagion of Cooperation in Static and Fluid Social Networks Cooperation is essential for successful human societies. Thus, understanding how cooperative and selfish behaviors spread from person to person is a topic of theoretical and practical importance. Previous laboratory experiments provide clear evidence of social contagion in the domain of cooperation, both in fixed networks and in randomly shuffled networks, but leave open the possibility of asymmetries in the spread of cooperative and selfish behaviors. Additionally, many real human interaction structures are dynamic: we often have control over whom we interact with. Dynamic networks may differ importantly in the goals and strategic considerations they promote, and thus the question of how cooperative and selfish behaviors spread in dynamic networks remains open. Here, we address these questions with data from a social dilemma laboratory experiment. We measure the contagion of both cooperative and selfish behavior over time across three different network structures that vary in the extent to which they afford individuals control over their network ties. We find that in relatively fixed networks, both cooperative and selfish behaviors are contagious. In contrast, in more dynamic networks, selfish behavior is contagious, but cooperative behavior is not: subjects are fairly likely to switch to cooperation regardless of the behavior of their neighbors. We hypothesize that this insensitivity to the behavior of neighbors in dynamic networks is the result of subjects' desire to attract new cooperative partners: even if many of one's current neighbors are defectors, it may still make sense to switch to cooperation. We further hypothesize that selfishness remains contagious in dynamic networks because of the well-documented willingness of cooperators to retaliate against selfishness, even when doing so is costly. These results shed light on the contagion of cooperative behavior in fixed and fluid networks, and have implications for influence-based interventions aiming at increasing cooperative behavior.

    Jillian J. Jordan, David G. Rand, Samuel Arbesman, James H. Fowler, Nicholas A. Christakis
    PLOS ONE 8 (6): e66199 (19 June 2013)

60. In Defense of Genopolitics The American Political Science Review recently published a critique of an article we published in the Journal of Politics in 2008. In that article we showed that variants of the genes 5HTT and MAOA were significantly associated with voter turnout in a sample of 2,300 subjects from the National Longitudinal Study of Adolescent Health. Here, we address the critique first by conducting a replication study using an independent sample of 9,300 subjects. These results show that the gene-environment interaction of the 5HTT gene variant with church attendance replicates, but the association with MAOA does not. We then focus on the general argument of the critique, showing that many of its characterizations of the literature in genetics and in political science are misleading or incorrect. We conclude by illustrating the ways genopolitics has already made a lasting contribution to the field of political science and by offering guidelines for future studies in genopolitics that are based on state-of-the-art recommendations from the field of behavior genetics.

    James H. Fowler, Christopher T. Dawes
    American Political Science Review 107 (2): 362–374 (May 2013)

61. Individual and neighborhood correlates of membership in drug using networks with a higher prevalence of HIV in New York City (2006–2009) Purpose
    To identify individual- and neighborhood-level correlates of membership within high HIV prevalence drug networks.
    Methods
    We recruited 378 New York City drug users via respondent-driven sampling (2006–2009). Individual-level characteristics and recruiter- recruit relationships were ascertained and merged with 2000 tract-level U.S. Census data. Descriptive statistics and population average models were used to identify correlates of membership in high HIV prevalence drug networks (>10.54% vs. <10.54% HIV).
    Results
    Individuals in high HIV prevalence drug networks were more likely to be recruited in neighborhoods with greater inequality (adjusted odds ratio [AOR], 5.85; 95% confidence interval [CI],1.40–24.42), higher valued owner-occupied housing (AOR, 1.48; 95% CI, 1.14–1.92), and a higher proportion of Latinos (AOR, 1.83; 95% CI, 1.19–2.80). They reported more crack use (AOR, 7.23; 95% CI, 2.43–21.55), exchange sex (AOR, 1.82; 95% CI, 1.03–3.23), and recent drug treatment enrollment (AOR, 1.62; 95% CI,1.05–2.50) and were less likely to report cocaine use (AOR, 0.40; 95% CI, 0.20–0.79) and recent home- lessness (AOR, 0.32; 95% CI, 0.17–0.57).
    Conclusions
    The relationship between exchange sex, crack use, and membership within high HIV prevalence drug networks may suggest an ideal HIV risk target population for intervention. Coupling network-based interventions with those adding risk-reduction and HIV testing/care/adherence counseling services to the standard of care in drug treatment programs should be explored in neighborhoods with increased inequality, higher valued owner-occupied housing, and a greater proportion of Latinos.

    Abby E. Rudolph, Natalie D. Crawford, Carl Latkin, James H. Fowler, Crystal M. Fuller
    Annals of Epidemiology 23 (5): 267–274 (May 2013)

62. Violent extremist group ecologies under stress Violent extremist groups are currently making intensive use of Internet fora for recruitment to terrorism. These fora are under constant scrutiny by security agencies, private vigilante groups, and hackers, who sometimes shut them down with cybernetic attacks. However, there is a lack of experimental and formal understanding of the recruitment dynamics of online extremist fora and the effect of strategies to control them. Here, we utilize data on ten extremist fora that we collected for four years to develop a data-driven mathematical model that is the first attempt to measure whether (and how) these external attacks induce extremist fora to self-regulate. The results suggest that an increase in the number of groups targeted for attack causes an exponential increase in the cost of enforcement and an exponential decrease in its effectiveness. Thus, a policy to occasionally attack large groups can be very efficient for limiting violent output from these fora.

    Manuel Cebrian, Manuel R. Torres, Ramon Huerta, James H. Fowler
    Scientific Reports 3: 1544 (27 March 2013)

63. Red Brain, Blue Brain: Evaluative Processes Differ in Democrats and Republicans Liberals and conservatives exhibit different cognitive styles and converging lines of evidence suggest that biology influences differences in their political attitudes and beliefs. In particular, a recent study of young adults suggests that liberals and conservatives have significantly different brain structure, with liberals showing increased gray matter volume in the anterior cingulate cortex, and conservatives showing increased gray matter volume in the in the amygdala. Here, we explore differences in brain function in liberals and conservatives by matching publicly-available voter records to 82 subjects who performed a risk-taking task during functional imaging. Although the risk-taking behavior of Democrats (liberals) and Republicans (conservatives) did not differ, their brain activity did. Democrats showed significantly greater activity in the left insula, while Republicans showed significantly greater activity in the right amygdala. In fact, a two parameter model of partisanship based on amygdala and insula activations yields a better fitting model of partisanship than a well-established model based on parental socialization of party identification long thought to be one of the core findings of political science. These results suggest that liberals and conservatives engage different cognitive processes when they think about risk, and they support recent evidence that conservatives show greater sensitivity to threatening stimuli.

    Darren Schreiber, Greg Fonzo, Alan N. Simmons, Christopher T. Dawes, Taru Flagan, James H. Fowler, Martin P. Paulus
    PLOS ONE 8 (2): e52970 (13 February 2013)
    • Time
    • Wall Street Journal
    • UPI

64. A Random World Is a Fair World A preference for fairness or equity in the distribution of resources influences many human decisions. The origin of this preference is a topic that has consumed philosophers, social scientists, and biologists for centuries. However, although we feel a sense of fairness deeply and intuitively, it has so far been difficult to explain from first principles how such a feeling might have evolved. How could natural selection allow for the survival of "fair" individuals who sometimes give things away to equalize resources when they must compete with self-interested individuals who keep everything for themselves? In PNAS, Rand et al. provide a unique and compelling solution to this puzzle: it's all because of dumb luck.

    James H. Fowler, Nicholas A. Christakis
    PNAS 110 (7): 2440–2441 (12 February 2013)

65. Yahtzee: An Anonymized Group Level Matching Procedure Researchers often face the problem of needing to protect the privacy of subjects while also needing to integrate data that contains personal information from diverse data sources. The advent of computational social science and the enormous amount of data about people that is being collected makes protecting the privacy of research subjects ever more important. However, strict privacy procedures can hinder the process of joining diverse sources of data that contain information about specific individual behaviors. In this paper we present a procedure to keep information about specific individuals from being "leaked" or shared in either direction between two sources of data without need of a trusted third party. To achieve this goal, we randomly assign individuals to anonymous groups before combining the anonymized information between the two sources of data. We refer to this method as the Yahtzee procedure, and show that it performs as predicted by theoretical analysis when we apply it to data from Facebook and public voter records.

    Jason J. Jones, Robert M. Bond, Christopher J. Fariss, Jaime E. Settle, Adam D. I. Kramer, Cameron Marlow, James H. Fowler
    PLOS ONE 8 (2): e55760 (5 February 2013)
    • R Code for Yahtzee Procedure

66. Social Contagion Theory: Examining Dynamic Social Networks and Human Behavior Here, we review the research we have done on social contagion. We describe the methods we have employed (and the assumptions they have entailed) in order to examine several datasets with complementary strengths and weaknesses, including the Framingham Heart Study, the National Longitudinal Study of Adolescent Health, and other observational and experimental datasets. We describe the regularities that led us to propose that human social networks may exhibit a "three degrees of influence" property, and we review statistical approaches we have used to characterize inter-personal influence with respect to behaviors like obesity and affective states like happiness. We do not claim that this work is the final word, but we do believe that it provides some novel, informative, and stimulating evidence regarding social contagion in longitudinally followed networks. Along with other scholars, we are working to develop new methods for identifying causal effects using social network data, and we believe that this area is ripe for statistical development as current methods have known and often unavoidable limitations.

    Nicholas A. Christakis, James H. Fowler
    Statistics in Medicine 32 (4): 556–577 (February 2013)
    • Reply to Commentaries

67. Born to Lead? A Twin Design and Genetic Association Study of Leadership Role Occupancy We address leadership emergence and the possibility that there is a partially innate predisposition to occupy a leadership role. Employing twin design methods on data from the National Longitudinal Study of Adolescent Health, we estimate the heritability of leadership role occupancy at 24%. Twin studies do not point to specific genes or neurological processes that might be involved. We therefore also conduct association analysis on the available genetic markers. The results show that leadership role occupancy is associated with rs4950, a single nucleotide polymorphism (SNP) residing on a neuronal acetylcholine receptor gene (CHRNB3). We replicate this family-based genetic association result on an independent sample in the Framingham Heart Study. This is the first study to identify a specific genotype associated with the tendency to occupy a leadership position. The results suggest that what determines whether an individual occupies a leadership position is the complex product of genetic and environmental influences; with a particular role for rs4950.

    Jan-Emmanuel De Neve, Slava Mikhaylov, Christopher T. Dawes, Nicholas A. Christakis, James H. Fowler
    The Leadership Quarterly 24 (1): 45–60 (February 2013)
    • CBC News
    • The Independent

68. Inferring Tie Strength from Online Directed Behavior Some social connections are stronger than others. People have not only friends, but also best friends. Social scientists have long recognized this characteristic of social connections and researchers frequently use the term tie strength to refer to this concept. We used online interaction data (specifically, Facebook interactions) to successfully identify real-world strong ties. Ground truth was established by asking users themselves to name their closest friends in real life. We found the frequency of online interaction was diagnostic of strong ties, and interaction frequency was much more useful diagnostically than were attributes of the user or the user's friends. More private communications (messages) were not necessarily more informative than public communications (comments, wall posts, and other interactions).

    Jason J. Jones, Jaime E. Settle, Robert M. Bond, Christopher J. Fariss, Cameron Marlow, James H. Fowler
    PLOS ONE 8 (1): e52168 (2 January 2013)
    • The Atlantic
    • The Today Show

69. Strategic Citations to Precedent on the U.S. Supreme Court The Common Law evolves not only through the outcomes of cases, but also through the reasoning and citations to precedent employed in judicial opinions. We focus on citations to precedent by the U.S. Supreme Court. We demonstrate how strategic interaction between justices during the Court's bargaining process affects citations to precedent in the Court's opinion. We find that the majority opinion writer relies more heavily on precedent when the Court's decision is accompanied by separate opinions. We also show that diversity of opinion on the Court, a factor often overlooked, has a significant relationship with citations to precedent. Finally, our results indicate that the ideology of the median justice influences citation practices more so than the majority opinion writer's ideology.

    Yonatan Lupu, James H. Fowler
    Journal of Legal Studies 42 (1): 151–186 (January 2013)
    • Replication Data

70. Parental Influence on Substance Use in Adolescent Social Networks Objectives
    Both peer and parental influences have been associated with the use of addictive substances in adolescence. We evaluated the relationship between the parenting style of an adolescent's peers' parents and an adolescent's substance use.
    Design
    Longitudinal survey
    Setting
    Adolescents across the United States were interviewed at school and at home
    Participants
    Nationally representative sample of adolescents in the United States
    Main Exposure
    Authoritative versus neglectful parenting style of adolescent's parents and adolescent's friends parents; adolescent substance use
    Main Outcome Measures
    Adolescent alcohol abuse, smoking, marijuana use, and binge drinking
    Results
    If an adolescent has a friend whose mother is authoritative, that adolescent is 40% (95% CI 12%-58%) less likely to drink to the point of drunkenness, 38% (95% CI 5%-59%) less likely to binge drink, 39% (95% CI 12%-58%) less likely to smoke cigarettes, and 43% (95% CI 1%-67%) less likely to use marijuana than an adolescent whose friend's mother is neglectful, controlling for the parenting style of the adolescent's own mother, school level fixed effects, and demographics. These results are only partially mediated by peer substance use.
    Conclusion
    Social network influences may extend beyond the homogeneous dimensions of own-peer or own-parent to include extra-dyadic influences of the wider network. The value of parenting interventions should be re-assessed to take into account these spillover effects in the greater network.

    Holly B. Shakya, Nicholas A. Christakis, James H. Fowler
    Archives of Pediatrics & Adolescent Medicine 166 (12): 1132–1139 (December 2012)
    • U.S. News

71. The Evolution of Homophily Biologists have devoted much attention to assortative mating or homogamy, the tendency for sexual species to mate with similar others. In contrast, there has been little theoretical work on the broader phenomenon of homophily, the tendency for individuals to interact with similar others. Yet this behaviour is also widely observed in nature. Here, we model how natural selection can give rise to homophily when individuals engage in social interaction in a population with multiple observable phenotypes. Payoffs to interactions depend on whether or not individuals have the same or different phenotypes, and each individual has a preference that determines how likely they are to interact with others of their own phenotype (homophily) or of opposite phenotypes (heterophily). The results show that homophily tends to evolve under a wide variety of conditions, helping to explain its ubiquity in nature.

    Feng Fu, Martin A. Nowak, Nicholas A. Christakis, James H. Fowler
    Scientific Reports 2: 845 (13 November 2012)
    • Supplementary Information
    • Harvard Gazette

72. Genes, Economics, and Happiness We explore the influence of genetic variation on subjective well-being by employing a twin design and genetic association study. In a nationally- representative twin sample, we first show that about 33% of the variation in life satisfaction is explained by genetic variation. Although previous stud- ies have shown that baseline happiness is significantly heritable, little research has considered molecular genetic associations with subjective well-being. We study the relationship between a functional polymorphism on the serotonin transporter gene (5-HTTLPR) and life satisfaction. We initially find that individuals with the longer, transcriptionally more efficient variant of this genotype report greater life satisfaction (n=2,545, p=0.012). However, our replication attempts on independent samples produce mixed results indicat- ing that more work needs to be done to better understand the relationship between this genotype and subjective well-being. This work has implications for how economists think about the determinants of utility, and the extent to which exogenous shocks might affect individual well-being.

    Jan-Emmanuel De Neve, Nicholas A. Christakis, James H. Fowler, Bruno Frey
    Journal of Neuroscience, Psychology, and Economics 5 (4): 193–211 (November 2012)
    • The Economist
    • Psychology Today

73. A 61-Million-Person Experiment in Social Influence and Political Mobilization Human behaviour is theorized to spread via face-to-face social networks, but it is difficult to identify social influence effects in observational studies and it is unknown whether online social networks operate in the same way. Here, we report results from a randomized controlled trial of political mobilization messages delivered to 61 million Facebook users during the 2010 U.S. Congressional elections. The results show that the messages directly influenced political self-expression, information seeking, and real world voting behaviour of millions of people. Furthermore, the messages not only influenced the users who received them, but the users' friends and friends of friends as well. The effect of social transmission on real world voting was larger than the direct effect of the messages themselves, and nearly all the transmission occurred between "close friends" who were more likely to have a face-to-face relationship. These results suggest that strong ties are instrumental for spreading both online and real world behaviour in human social networks.

    Robert M. Bond, Christopher J. Fariss, Jason J. Jones, Adam D. I. Kramer, Cameron Marlow, Jaime E. Settle, James H. Fowler
    Nature 489: 295–298 (13 September 2012)
    • Supplementary Information
    • PowerPoint Slides
    • Commentary by Sinan Aral
    • Top Ten Social Media Papers of 2012
    • New York Times
    • Washington Post
    • NPR All Things Considered
    • NPR Science Friday
    • PBS Newshour
    • Time
    • MSNBC
    • CNN
    • UCSD Press Release

74. Egocentric Social Network Structure, Health, and Pro-Social Behaviors in a National Panel Study of Americans Using a population-based, panel survey, we study how egocentric social networks change over time, and the relationship between egocentric network properties and health and pro-social behaviors. We find that the number of prosocial activities is strongly positively associated with having more friends, or an increase in degree, with approximately 0.04 more prosocial behaviors expected for every friend added. Moreover, having more friends is associated with an improvement in health, while being healthy and prosocial is associated with closer relationships. Specifically, a unit increase in health is associated with an expected 0.45 percentage-point increase in average closeness, while adding a prosocial activity is associated with a 0.46 percentage-point increase in the closeness of one's relationships. Furthermore, a tradeoff between degree and closeness of social contacts was observed. As the number of close social contacts increases by one, the estimated average closeness of each individual contact decreases by approximately three percentage-points. The increased awareness of the importance of spillover effects in health and health care makes the ascertainment of egocentric social networks a valuable complement to investigations of the relationship between socioeconomic factors and health.

    A. James O'Malley, Samuel Arbesman, Darby Miller Steiger, James H. Fowler, Nicholas A. Christakis
    PLOS ONE 7 (5): e36250 (15 May 2012)
    • Wired

75. Life Interwoven Biologist E. O. Wilson's brilliant new volume, The Social Conquest of Earth, could more aptly be entitled 'Biology's Conquest of Science'. Drawing on his deep understanding of entomology and his extraordinarily broad knowledge of the natural and social sciences, Wilson makes a strong case for the synthesis of knowledge across disciplines. Understanding the biological origin of what makes us human can help us to build better theories of social and psychological interaction; in turn, understanding how other social species have evolved may help us to better understand the origin of our own. But the main reason that Wilson's book is successful is that he also brings into biology the best of what social science has to offer. He draws on careful work in linguistics, psychology, economics, religious studies and the arts to elaborate on differences between humans and other species. This give and take, this flow of ideas across disciplines, allows him to study an intriguing set of questions. Why did ants and humans both become social? What is it about being social that helped both species to achieve evolutionary success? And if it worked so well, why aren't all other species like us?

    James H. Fowler
    Nature 484: 448–449 (26 April 2012)

76. The Neural Basis of Egalitarian Behavior Individuals are willing to sacrifice their own resources to promote equality in groups. These costly choices promote equality and are associated with behavior that supports cooperation in humans, but little is known about the brain processes involved. We use functional MRI to study egalitarian preferences based on behavior observed in the "random income game." In this game, subjects decide whether to pay a cost to alter group members' randomly allocated incomes. We specifically examine whether egalitarian behavior is associated with neural activity in the ventromedial prefrontal cortex and the insular cortex, two regions that have been shown to be related to social preferences. Consistent with previous studies, we find significant activation in both regions; however, only the insular cortex activations are significantly associated with measures of revealed and expressed egalitarian preferences elicited outside the scanner. These results are consistent with the notion that brain mechanisms involved in experiencing the emotional states of others underlie egalitarian behavior in humans.

    Christopher T. Dawes, Peter J. Loewen, Darren Schreiber, Alan N. Simmons, Taru Flagan, Richard McElreath, Scott E. Bokemper, James H. Fowler, Martin P. Paulus
    PNAS 109 (17): 6479–6483 (24 April 2012)
    • Supplementary Information

77. Aspirin Use and Cardiovascular Events in Social Networks We tested whether friends' and family members' cardiovascular health events and also their own aspirin use are associated with the likelihood that an individual takes aspirin regularly. Analyses were based on longitudinal data on 2,724 members of the Framingham Heart Study (based in Massachusetts, U.S.A) who were linked to friends and family members who were also participants in the same study. Men were more likely to take aspirin if a male friend had recently been taking aspirin (OR 1.48, 95% CI 1.03, 2.13), and women were more likely to take aspirin if a brother (OR 1.35, 95% CI 1.03, 1.77) had recently been taking aspirin. Men were also more likely to take aspirin if a brother recently had a cardiovascular event (OR 1.41, 95% CI 1.04, 1.93), and women were more likely to take aspirin if a female friend recently experienced a cardiovascular event (OR 2.85, 95% CI 1.27, 6.37). Aspirin use is correlated with the health and behavior of friends and family. These findings add to a growing body of evidence, which suggests that behavioral changes that promote cardiovascular health may spread through social networks.

    Kate W. Strully, James H. Fowler, Joanne Murabito, Emelia J. Benjamin, Daniel Levy, Nicholas A. Christakis
    Social Science & Medicine 74 (7): 1125–1129 (March 2012)

78. Modeling Dynamical Influence in Human Interaction How can we model influence between individuals in a social system, even when the network of interactions is unknown? In this article, we review the literature on the "influence model," which utilizes independent time series to estimate how much the state of one actor affects the state of another actor in the system. We extend this model to incorporate dynamical parameters that allow us to infer how influence changes over time, and we provide three examples of how this model can be applied to simulated and real data. The results show that the model can recover known estimates of influence, it generates results that are consistent with other measures of social networks, and it allows us to uncover important shifts in the way states may be transmitted between actors at different points in time.

    Wei Pan, Wen Dong, Manuel Cebrian, Taemie Kim, James H. Fowler, Alex (Sandy) Pentland
    IEEE Signal Processing Magazine 29 (2): 77–86 (March 2012)
    • Technology Review

79. Social Networks and Cooperation in Hunter-Gatherers Social networks show striking structural regularities, and both theory and evidence suggest that networks may have facilitated the development of large-scale cooperation in humans. Here, we characterize the social networks of the Hadza, a population of hunter-gatherers in Tanzania. We show that Hadza networks have important properties also seen in modernized social networks, including a skewed degree distribution, degree assortativity, transitivity, reciprocity, geographic decay and homophily. We demonstrate that Hadza camps exhibit high between-group and low within-group variation in public goods game donations. Network ties are also more likely between people who give the same amount, and the similarity in cooperative behaviour extends up to two degrees of separation. Social distance appears to be as important as genetic relatedness and physical proximity in explaining assortativity in cooperation. Our results suggest that certain elements of social network structure may have been present at an early point in human history. Also, early humans may have formed ties with both kin and non-kin, based in part on their tendency to cooperate. Social networks may thus have contributed to the emergence of cooperation.

    Coren L. Apicella, Frank W. Marlowe, James H. Fowler, Nicholas A. Christakis
    Nature 477: 497–501 (26 January 2012)
    • Supplementary Information
    • YouTube video of fieldwork with the Hadza
    • 3D Movie of the Female Hadza Network
    • 3D Movie of the Male Hadza Network
    • Commentary by Joe Henrich
    • Los Angeles Times
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80. Molecular Genetics and Economics In this article, we describe the new field of "genoeconomics," the use of molecular genetic information in economics. To illustrate some of the challenges that researchers in this field are likely to encounter, we present results from a "genome-wide association study" (GWAS) of educational attainment, one of the first of its kind in economics. This type of study involves analyzing hundreds of thousands of genetic markers and seeking to understand their association with some trait of interest. We use a sample of 7,500 individuals from the Framingham Heart Study. After quality controls, our dataset contains over 360,000 genetic markers per person. Despite some initially promising results, the main findings from this dataset fail to replicate in a second large replication sample of 9,500 people from the Rotterdam Study, suggesting that the original results were probably spurious. These findings are unfortunately typical in these types of studies of molecular genetics and therefore also cautionary.

    Jonathan P. Beauchamp, David Cesarini, Magnus Johannesson, Matthijs J. H. M. van der Loos, Philipp D. Koellinger, Patrick J. F. Groenen, James H. Fowler, J. Niels Rosenquist, A. Roy Thurik, Nicholas A. Christakis
    Journal of Economic Perspectives 25 (4): 1–27 (Fall 2011)

81. The Evolution of Overconfidence Confidence is an essential ingredient of success in a wide range of domains ranging from job performance and mental health to sports, business and combat. Some authors have suggested that not just confidence but overconfidence -- believing you are better than you are in reality -- is advantageous because it serves to increase ambition, morale, resolve, persistence or the credibility of bluffing, generating a self-fulfilling prophecy in which exaggerated confidence actually increases the probability of success. However, overconfidence also leads to faulty assessments, unrealistic expectations and hazardous decisions, so it remains a puzzle how such a false belief could evolve or remain stable in a population of competing strategies that include accurate, unbiased beliefs. Here we present an evolutionary model showing that, counterintuitively, overconfidence maximizes individual fitness and populations tend to become overconfident, as long as benefits from contested resources are sufficiently large compared with the cost of competition. In contrast, unbiased strategies are only stable under limited conditions. The fact that overconfident populations are evolutionarily stable in a wide range of environments may help to explain why overconfidence remains prevalent today, even if it contributes to hubris, market bubbles, financial collapses, policy failures, disasters and costly wars.

    Dominic D. P. Johnson, James H. Fowler
    Nature 477: 317–320 (15 September 2011)
    • Supplementary Information
    • R code for simulations
    • Commentary by Matthijs van Veelen and Martin Nowak
    • Our SEED Op-Ed
    • Discover Magazine's Top 100 Stories of 2011
    • National Geographic
    • Nature Podcast
    • Discovery News
    • MSNBC

82. Social Preferences and Political Participation Models of political participation have begun to incorporate actors who possess social preferences. However, these models have failed to take into account the potentially incongruent political goals of different social preference types. These goals are likely to play an important role in shaping political behavior. To examine the effect of distinct social preferences on political activity we conducted an experiment in which participants played five rounds of a modified dictator game (Andreoni and Miller 2002). We used the decisions in these games to determine their preference type and mapped these types to reported political activity. Our results show that subjects who were most interested in increasing total welfare in the dictator game were more likely to participate in politics than subjects with selfish preferences, whereas sub jects most interested in reducing the difference between their own well-being and the well-being of others were no more likely to participate.

    Christopher T. Dawes, Peter J. Loewen, James H. Fowler
    Journal of Politics 73 (3): 845–856 (July 2011)

83. Contagion in Prescribing Behavior Among Networks of Doctors A foundational study regarding the diffusion of innovation involved the adoption of tetracycline by doctors in four mid-western communities in the 1950s (Coleman, Katz, and Menzel 1966), and it is not a coincidence that social scientists keep returning to this particular application of social network analysis (including to re-analyze this original study by Coleman and colleagues (Van den Bulte and Lilien 2001)). Studying the use of drugs by doctors involves the perfect mix of a discernable social network (among the doctors), a distinct innovation (a drug), an important area (patient care), difficult statistics (related to causal inference), and financial stakes (by pharmaceutical companies, insurers, and others). Iyengar, Van den Bulte, and Valente, in their careful and insightful study, find that even after controlling for marketing effort and arbitrary system-wide changes, there is evidence for contagion in the prescribing patterns of doctors. The modeling is excellent, including controls for secular trends (such as the emergence of new drugs or clinical evidence or a change in prevalence of the disease), and the conceptual framework is innovative and comprehensive. And so this paper represents another important link in the chain stretching back to Coleman.

    Nicholas A. Christakis, James H. Fowler
    Marketing Science 30 (2): 213–216 (March–April 2011)

84. Social Network Determinants of Depression The etiology of depression has long been thought to include social environmental factors. To quantitatively explore the novel possibility of person-to-person spread and network-level determination of depressive symptoms, analyses were performed on a densely interconnected social network of 12,067 people assessed repeatedly over 32 years as part of the Framingham Heart Study. Longitudinal statistical models were used to examine whether depressive symptoms in one person were associated with similar scores in friends, co-workers, siblings, spouses and neighbors. Depressive symptoms were assessed using CES-D scores that were available for subjects in three waves measured between 1983 and 2001. Results showed both low and high CES-D scores (and classification as being depressed) in a given period were strongly correlated with such scores in one's friends and neighbors. This association extended up to three degrees of separation (to one's friends' friends' friends). Female friends appear to be especially influential in the spread of depression from one person to another. The results are robust to multiple network simulation and estimation methods, suggesting that network phenomena appear relevant to the epidemiology of depression and would benefit from further study.

    J. Niels Rosenquist, James H. Fowler, Nicholas A. Christakis
    Molecular Psychiatry 16 (3): 273–281 (March 2011)
    • Supplementary Information

85. Causality in Political Networks As the study of political networks becomes more common in political science, greater attention to questions of causality is warranted. This essay explores competing visions of causality in political networks. Independent essays address issues of statistical model specification, identification of multi-step personal influence, measurement error, causality in historical perspective, and the insights of field experiments. These essays do not agree entirely on the nature of causality in political networks, though they commonly take seriously concerns regarding homophily, time-consistency, and the uniqueness of political network data. Serious consideration of these methodological issues promises to enhance the value-added of network analysis in the study of politics.

    James H. Fowler, Michael T. Heaney, David W. Nickerson, John F. Padgett, Betsy Sinclair
    American Politics Research 39 (2): 437–480 (March 2011)
    • R code for Monte Carlo simulations

86. Correlated Genotypes in Friendship Networks It is well known that humans tend to associate with other humans who have similar characteristics, but it is unclear whether this tendency has consequences for the distribution of genotypes in a population. Although geneticists have shown that populations tend to stratify genetically, this process results from geographic sorting or assortative mating, and it is unknown whether genotypes may be correlated as a consequence of non-reproductive associations or other processes. Here, we study six available genotypes from the National Longitudinal Study of Adolescent Health to test for genetic similarity between friends. Maps of the friendship networks show clustering of genotypes, and, after we apply strict controls for population stratification, the results show that one genotype is positively correlated (homophily) and one genotype is negatively correlated (heterophily). A replication study on an independent sample from the Framingham Heart Study verifies that DRD2 exhibits significant homophily and that CYP2A6 exhibits significant heterophily. These novel results show that homophily and heterophily obtain on a genetic (indeed, an allelic) level, which has implications for the study of population genetics and social behavior. In particular, the results suggest that association tests should include friends' genes and that theories of evolution should take into account the fact that humans might, in some sense, be "metagenomic" with respect to the humans around them.

    James H. Fowler, Jaime E. Settle, Nicholas A. Christakis
    PNAS 108 (5): 1993–1997 (1 February 2011)
    • Supplementary Appendix
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87. Genes, Games, and Political Participation This chapter argues that the puzzle of cooperation is very closely related to two of our most important questions in political science: 1) How do we organize ourselves to do more than we could on our own? and 2) How do we distribute the fruits of our collective labor? In this chapter we argue that the answers to these questions can be better understood by considering models of early cooperation in pre-modern times. As we show, the emergence of cooperation relied on a population with different types of people, some of whom were inclined towards taking up costly action for the benefit of others. We also review the use of laboratory experiments from behavioral economics to show that differences between individuals can explain variation in large-scale cooperative acts like voting and other forms of political participation that take place in modern times. And finally, we explore the root of these different types of behavior. Although much of our political behavior is learned and influenced by the environment, we are quickly coming to realize that fundamental differences in participation and political ideology reach deep into our biology, in some cases all the way to our DNA.

    James H. Fowler, Peter J. Loewen, Jaime E. Settle, Christopher T. Dawes,
    in Man Is by Nature a Political Animal: Evolution, Biology, and Politics, eds. Peter K. Hatemi, Rose McDermott, Chicago University Press, 207–223 (2011)

88. Distance Measures for Dynamic Citation Networks Acyclic digraphs arise in many natural and artificial processes. Among the broader set, dynamic citation networks represent a substantively important form of acyclic digraphs. For example, the study of such networks includes the spread of ideas through academic citations, the spread of innovation through patent citations, and the development of precedent in common law systems. The specific dynamics that produce such acyclic digraphs not only differentiate them from other classes of graphs, but also provide guidance for meaningful analysis of these networks. We briefly discuss context-sensitive distance measures for nodes in a "citation" space and suggest potential applications for prediction and clustering.

    Michael J. Bommarito II, Daniel Martin Katz, Jon Zelner, James H. Fowler
    Physica A 389 (19): 4201–4208 (1 October 2010)
    • 3-D video of the evolution of the Supreme Court network
    • Network image of the Supreme Court network in 1815
    • Network image of the Supreme Court network in 1830

89. Friendships Moderate an Association Between a Dopamine Gene Variant and Political Ideology Scholars in many fields have long noted the importance of social context in the development of political ideology. Recent work suggests that political ideology also has a heritable component, but no specific gene variant associated with political ideology has so far been identified. In this article we hypothesize that individuals with a genetic predisposition towards seeking out new experiences will tend to be more liberal, but only if they are embedded in a social context that provides them with multiple points of view. Using data from the National Longitudinal Study of Adolescent Health, we test this hypothesis by investigating an association between self-reported political ideology and the 7R variant of the dopamine receptor D4 gene (DRD4), which has previously been associated with novelty-seeking. We find that the number of friendships a person has in adolescence is significantly associated with liberal political ideology among those with DRD4-7R. Among those without the gene variant there is no association. This is the first study ever to elaborate a specific gene-environment interaction that contributes to ideological self-identification, and it highlights the importance of incorporating both nature and nurture into the study of politics.

    Jaime E. Settle, Christopher T. Dawes, Nicholas A. Christakis, James H. Fowler
    Journal of Politics 72 (4): 1189–1198 (October 2010)
    • Supplementary Appendix
    • PBS
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    • Time
    • Science
    • UCSD Press Release

90. Social Network Sensors for Early Detection of Contagious Outbreaks Current methods for the detection of contagious outbreaks give contemporaneous information about the course of an epidemic at best. It is known that individuals near the center of a social network are likely to be infected sooner during the course of an outbreak, on average, than those at the periphery. Unfortunately, mapping a whole network to identify central individuals who might be monitored for infection is typically very difficult. We propose an alternative strategy that does not require ascertainment of global network structure, namely, simply monitoring the friends of randomly selected individuals. Such individuals are known to be more central. To evaluate whether such a friend group could indeed provide early detection, we studied an H1N1 flu outbreak at Harvard College in late 2009. We followed 744 students who were either members of a group of randomly chosen individuals or a group of their friends. Based on clinical diagnoses, the progression of the epidemic in the friend group occurred 13.9 days (95% C.I. 9.9–16.6) in advance of the randomly chosen group (i.e., the population as a whole). The friend group also showed a significant lead time (p<0.05) on day 16 of the epidemic, a full 46 days before the peak in daily incidence in the population as a whole. This sensor method could provide significant additional time to react to epidemics in small or large populations under surveillance. The amount of lead time will depend on features of the outbreak and the network at hand. The method could in principle be generalized to other biological, psychological, informational, or behavioral contagions that spread in networks.

    Nicholas A. Christakis, James H. Fowler
    PLOS ONE 5 (9): e12948 (15 September 2010)
    • Supplementary Information
    • Movie of the epidemic in QuickTime or MPEG4 format.
    • ISEE Best Paper Award
    • New York Times #2
    • The Economist
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91. The Behavioral Logic of Collective Action: Partisans Cooperate and Punish More Than Non-Partisans Why do individuals engage in personally costly, partisan activities that benefit others? If individuals act according to rational self-interest, then partisan activity occurs only when the benefits of that activity exceed its costs. However, laboratory experiments suggest that many people are willing to contribute to public goods and to punish those who do not contribute--even when these activities are personally costly and when members of the experimental group are completely anonymous. We hypothesize that these individuals, called strong reciprocators, underlie the capacity of political parties to organize competition for scarce resources and the production of public goods. To test this hypothesis, we conducted an experiment that includes a random income game with costly income alteration and a standard public goods game with costly punishment. These games allow us to gauge participants' willingness to contribute to public goods and to engage in the costly punishment of free-riders. The results show that partisans are more likely than nonpartisans to contribute to public goods and to engage in costly punishment. Thus, inherent tastes for cooperation and sanctioning help resolve the paradox of party participation.

    Oleg Smirnov, Christopher T. Dawes, James H. Fowler, Tim Johnson, Richard McElreath
    Political Psychology 31 (4): 595–616 (August 2010)
    • Data for the public goods game and random income game

92. The Spread of Alcohol Consumption Behavior in a Large Social Network Background
    Alcohol consumption has important health-related consequences and numerous biological and social determinants.
    Objective
    To explore quantitatively whether alcohol consumption behavior spreads from person to person in a large social network of friends, coworkers, siblings, spouses, and neighbors, followed for 32 years.
    Design
    Longitudinal network cohort study.
    Setting
    The Framingham Heart Study.
    Participants
    12 067 persons assessed at several time points between 1971 and 2003.
    Measurements
    Self-reported alcohol consumption (number of drinks per week on average over the past year and number of days drinking within the past week) and social network ties, measured at each time point.
    Results
    Clusters of drinkers and abstainers were present in the network at all time points, and the clusters extended to 3 degrees of separation. These clusters were not only due to selective formation of social ties among drinkers but also seem to reflect interpersonal influence. Changes in the alcohol consumption behavior of a person's social network had a statistically significant effect on that person's subsequent alcohol consumption behavior. The behaviors of immediate neighbors and coworkers were not significantly associated with a person's drinking behavior, but the behavior of relatives and friends was.
    Limitations
    A nonclinical measure of alcohol consumption was used. Also, it is unclear whether the effects on long-term health are positive or negative, because alcohol has been shown to be both harmful and protective. Finally, not all network ties were observed.
    Conclusion
    Network phenomena seem to influence alcohol consumption behavior. This has implications for clinical and public health interventions and further supports group-level interventions to reduce problematic drinking.

    J. Niels Rosenquist, Joanne Murabito, James H. Fowler, Nicholas A. Christakis
    Annals of Internal Medicine 152 (7): 426–433 (6 April 2010)
    • Appendix
    • Movie of the network
    • CNN
    • US News and World Report
    • Time

93. Cooperative Behavior Cascades in Human Social Networks Theoretical models suggest that social networks influence the evolution of cooperation, but to date there have been few experimental studies. Observational data suggest that a wide variety of behaviors may spread in human social networks, but subjects in such studies can choose to befriend people with similar behaviors, posing difficulty for causal inference. Here, we exploit a seminal set of laboratory experiments that originally showed that voluntary costly punishment can help sustain cooperation. In these experiments, subjects were randomly assigned to a sequence of different groups in order to play a series of single-shot public goods games with strangers; this feature allowed us to draw networks of interactions to explore how cooperative and uncooperative behavior spreads from person to person to person. We show that, in both an ordinary public goods game and in a public goods game with punishment, focal individuals are influenced by fellow group members' contribution behavior in future interactions with other individuals who were not a party to the initial interaction. Furthermore, this influence persists for multiple periods and spreads up to three degrees of separation (from person to person to person to person). The results suggest that each additional contribution a subject makes to the public good in the first period is tripled over the course of the experiment by other subjects who are directly or indirectly influenced to contribute more as a consequence. These are the first results to show experimentally that cooperative behavior cascades in human social networks.

    James H. Fowler, Nicholas A. Christakis
    PNAS 107 (12): 5334–5338 (23 March 2010)
    • Supporting Appendix
    • Replication Code and Data
    • CBS News
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    • UCSD Press Release

94. The Spread of Sleep Loss Influences Drug Use in Adolescent Social Networks Troubled sleep is a commonly cited consequence of adolescent drug use, but it has rarely been studied as a cause. Nor have there been any studies of the extent to which sleep behavior can spread in social networks from person to person to person. Here we map the social networks of 8,349 adolescents in order to study how sleep behavior spreads, how drug use behavior spreads, and how a friend's sleep behavior influences one's own drug use. We find clusters of poor sleep behavior and drug use that extend up to four degrees of separation (to one's friends' friends' friends' friends) in the social network. Prospective regression models show that being central in the network negatively influences future sleep outcomes, but not vice versa. Moreover, if a friend sleeps ≤7 hours, it increases the likelihood a person sleeps ≤7 hours by 11%. If a friend uses marijuana, it increases the likelihood of marijuana use by 110%. Finally, the likelihood that an individual uses drugs increases by 19% when a friend sleeps ≤7 hours, and a mediation analysis shows that 20% of this effect results from the spread of sleep behavior from one person to another. This is the first study to suggest that the spread of one behavior in social networks influences the spread of another. The results indicate that interventions should focus on healthy sleep to prevent drug use and targeting specific individuals may improve outcomes across the entire social network.

    Sara C. Mednick, Nicholas A. Christakis, James H. Fowler
    PLOS ONE 5 (3): e9775 (19 March 2010)
    • Supporting Information
    • New Scientist

95. Legislative Success in a Small World: Social Network Analysis and the Dynamics of Congressional Legislation We examine the social network structure of Congress from 1973-2004. We treat two Members of Congresas directly linked if they have cosponsored a bill together. We then construct explicit networks for each year using data from all forms of legislation, including resolutions, public and private bills, and amendments. We show that Congress exemplifies the characteristics of a "small world" network and that the varying small world properties during this time period are strongly related to the number of important bills passed.

    Wendy K. Tam Cho, James H. Fowler
    Journal of Politics 72 (1): 124–135 (January 2010)

96. Alone in the Crowd: The Structure and Spread of Loneliness in a Large Social Network The discrepancy between an individual's loneliness and the number of connections in a social network is well documented, yet little is known about the placement of loneliness within, or the spread of loneliness through, social networks. We use network linkage data from the population-based Framingham Heart Study to trace the topography of loneliness in people's social networks and the path through which loneliness spreads through these networks. Results indicated that loneliness occurs in clusters, extends up to three degrees of separation, is disproportionately represented at the periphery of social networks, and spreads through a contagious process. The spread of loneliness was found to be stronger than the spread of perceived social connections, stronger for friends than family members, and stronger for women than for men. The results advance our understanding of the broad social forces that drive loneliness and suggest that efforts to reduce loneliness in our society may benefit by aggressively targeting the people in the periphery to help repair their social networks and to create a protective barrier against loneliness that can keep the whole network from unraveling.

    John T. Cacioppo, James H. Fowler, Nicholas A. Christakis
    Journal of Personality & Social Psychology 97 (6): 977–991 (December 2009)
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    • High-resolution network image of loneliness in 2000
    • Science
    • Presentation Slides from the 2009 AAAS Annual Meeting

97. Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives Here we present intriguing evidence to show that our social networks drive and shape virtually every aspect of our lives. How we feel, whom we marry, whether we fall ill, how much money we make, and whether we vote all depend on what others around us—even those distantly connected to us—are doing, thinking, and feeling. We show that these connections have an ancient evolutionary past, and we describe how this will affect our new life as technology moves our networks online.

    Table of Contents

    1. In the Thick of It (intro)
    2. When You Smile, the World Smiles with You (emotions)
    3. Love the One You're With (love and sex)
    4. This Hurts Me as Much as It Hurts You (health)
    5. The Buck Starts Here (money)
    6. Politically Connected (politics)
    7. It's in Our Nature (evolution)
    8. Hyperconnected (technology)
    9. The Whole Is Great (conclusion)

    (book)

    Nicholas A. Christakis, James H. Fowler
    Little Brown (28 September 2009)
    • Books for a Better Life Award
    • Business Week Best Books of 2009
    • New York Times Book Review Editor's Choice
    • Oprah's Fall Reading Guide
    • Book Expo America favorite "Buzz" book
    • Review in New York Times Book Review
    • Review in New Scientist
    • Review in Science News
    • Our Los Angeles Times op-ed
    • New York Times Magazine cover story
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    • Powerpoint slides from BookTV presentation

98. The Heritability of Partisan Attachment One of the strongest regularities in the empirical political science literature is the well-known correlation in parent and child partisan behavior. Until recently this phenomenon was thought to result solely from parental socialization, but new evidence on genetic sources of behavior suggests it might also be due to heritability. In this article we hypothesize that genes contribute to variation in a general tendency toward strength of partisanship. Using data collected at the Twins Days Festival in Twinsburg, Ohio in 2006 and 2007, we compare the similarity of partisan strength in identical twins (who share all of their genes) to the similarity of partisan strength in non-identical twins (who share only half). The results show that heritability accounts for almost half of the variance in strength of partisan attachment, and they suggest that we should pay closer attention to the role of biology in the expression of important political behaviors.

    Jaime E. Settle, Christopher T. Dawes, James H. Fowler
    Political Research Quarterly 62 (3): 601–613 (September 2009)
    • Science

99. Partisanship, Voting, and the Dopamine D2 Receptor Gene Previous studies have found that both political orientations (Alford, Funk and Hibbing 2005) and voting behavior (Fowler, Baker and Dawes 2008; Fowler and Dawes 2008) are significantly heritable. In this article we study genetic variation in another important political behavior: partisan attachment. Using the National Longitudinal Study of Adolescent Health, we show that individuals with the A2 allele of the D2 dopamine receptor gene are significantly more likely to identify as a partisan than those with the A1 allele. Further, we find that this gene's association with partisanship also mediates an indirect association between the A2 allele and voter turnout. These results are the first to identify a specific gene that may be partly responsible for the tendency to join political groups, and they may help to explain correlation in parent and child partisanship and the persistence of partisan behavior over time.

    Christopher T. Dawes, James H. Fowler
    Journal of Politics 71 (3): 1157–1171 (July 2009)
    • New York Times editorial

100. The Role of Egalitarian Motives in Altruistic Punishment Altruistic punishment increases cooperation in human social exchange. However, the mechanisms underlying punishment remain in question. Punishment is consistent with both a desire to enforce cooperative norms and an egalitarian motive seeking to eliminate income disparities. Recent evidence indicates that egalitarian motives yield behavior that resembles costly punishment: individuals are willing to alter others' incomes, at a considerable cost, in order to attain equality. This work, however, only hints at a link between egalitarian preferences and altruistic punishment. Here we conduct experiments in which subjects participate in both a game that measures individuals' preferences for income equality and a modified public goods game that magnifies the influence of sanctioning motives. Controlling for income differences and the order of experiments, our results provide the first direct laboratory evidence that the same individuals who care about equality are those who are most willing to punish free-riders in public goods games. In an independent replication, we also show that egalitarian motives predict altruistic punishment behavior in a standard public goods game. Inequality aversion thus appears to play an important role in the income-altering behavior that facilitates cooperation in human groups.

     Tim Johnson, Christopher T. Dawes, James H. Fowler, Richard McElreath, Oleg Smirnov
     Economics Letters 102 (3): 192–194 (March 2009)
     • Online Appendix

101. Model of Genetic Variation in Human Social Networks Social networks influence the evolution of cooperation and they exhibit strikingly systematic patterns across a wide range of human contexts. Both of these facts suggest that variation in the topological attributes of human social networks might have a genetic basis. While genetic variation accounts for a significant portion of the variation in many complex social behaviors, the heritability of egocentric social network attributes is unknown. Here we show that three of these attributes (in-degree, transitivity, and centrality) are heritable. We then develop a 'mirror network' method to test extant network models and show that none accounts for observed genetic variation in human social networks. We propose an alternative 'attract and introduce' model that generates significant heritability as well as other important network features, and we show that this model with two simple forms of heterogeneity is well suited to the modeling of real social networks in humans.! These results suggest that natural selection may have played a role in the evolution of social networks. They also suggest that modeling intrinsic variation in network attributes may be important for understanding the way genes affect human behaviors and the way these behaviors spread from person to person.

     James H. Fowler, Christopher T. Dawes, Nicholas A. Christakis
     PNAS 106 (6): 1720–1724 (10 February 2009)
     • Supplementary Information
     • Online Appendix
     • Commentary by Matthew O. Jackson
     • Wall Street Journal
     • UCSD Press Release
     • Slides from Sunbelt 2009 Presentation

102. Computational Social Science We live life in the network. We check our e-mails regularly, make mobile phone calls from almost any location, swipe transit cards to use public transportation, and make purchases with credit cards. Our movements in public places may be captured by video cameras, and our medical records stored as digital files. We may post blog entries accessible to anyone, or maintain friendships through online social networks. Each of these transactions leaves digital traces that can be compiled into comprehensive pictures of both individuals and group behavior, with the potential to transform our understanding of our lives, organizations, and societies.

     David Lazer, Alex (Sandy) Pentland, Lada Adamic, Sinan Aral, Albert-László Barabási, Devon Brewer, Nicholas Christakis, Noshir Contractor, James H. Fowler, Myron Gutmann, Tony Jebara, Gary King, Michael Macy, Deb Roy, Marshall Van Alstyne
     Science 323 (5919): 721–723 (6 February 2009)
     • Supplementary Information

103. Social Network Visualization in Epidemiology Epidemiological investigations and interventions are increasingly focusing on social networks. Two aspects of social networks are relevant in this regard: the structure of networks and the function of networks. A better understanding of the processes that determine how networks form and how they operate with respect to the spread of behavior holds promise for improving public health. Visualizing social networks is a key to both research and interventions. Network images supplement statistical analyses and allow the identification of groups of people for targeting, the identification of central and peripheral individuals, and the clarification of the macro-structure of the network in a way that should affect public health interventions. People are inter-connected and so their health is inter-connected. Inter-personal health effects in social networks provide a new foundation for public health.

     Nicholas A. Christakis, James H. Fowler
     Norwegian Journal of Epidemiology 19 (1): 5–16 (2009)

104. Dynamic Spread of Happiness in a Large Social Network: Longitudinal Analysis Over 20 Years in the Framingham Heart Study Objectives
     To evaluate whether happiness can spread from person to person and whether niches of happiness form within social networks.
     Design
     Longitudinal social network analysis.
     Setting
     Framingham Heart Study social network.
     Participants
     4739 individuals followed from 1983 to 2003.
     Main outcome measures
     Happiness measured with validated four item scale; broad array of attributes of social networks and diverse social ties.
     Results
     Clusters of happy and unhappy people are visible in the network, and the relationship between people's happiness extends up to three degrees of separation (for example, to the friends of one's friends' friends). People who are surrounded by many happy people and those who are central in the network are more likely to become happy in the future. Longitudinal statistical models suggest that clusters of happiness result from the spread of happiness and not just a tendency for people to associate with similar individuals. A friend who lives within a mile (about 1.6 km) and who becomes happy increases the probability that a person is happy by 25% (95% confidence interval 1% to 57%). Similar effects are seen in coresident spouses (8%, 0.2% to 16%), siblings who live within a mile (14%, 1% to 28%), and next door neighbours (34%, 7% to 70%). Effects are not seen between coworkers. The effect decays with time and with geographical separation.
     Conclusions
     People's happiness depends on the happiness of others with whom they are connected. This provides further justification for seeing happiness, like health, as a collective phenomenon.

     James H. Fowler, Nicholas A. Christakis
     British Medical Journal 337: a2338 (4 December 2008)
     • Supplementary Information
     • High-resolution network image of happiness in 2000
     • High-resolution network image of happiness in 1996
     • Commentary by Peter Sainsbury
     • Boston Globe front page
     • Los Angeles Times front page
     • New York Times, including Quotation of the Day
     • NPR Science Friday
     • NBC Nightly News
     • Good Morning America
     • The Colbert Report
     • UCSD Press Release

105. Biology, Politics, and the Emerging Science of Human Nature In the past fifty years, biologists have learned a tremendous amount about human brain function and its genetic basis. At the same time political scientists have been intensively studying the effect of the social and institutional environment on mass political attitudes and behaviors. However, these separate fields of inquiry are subject to inherent limitations that may only be resolved through collaboration across disciplines. Here we describe recent advances in the emerging fields of genopolitics and neuropolitics and argue that biologists and political scientists must work together to advance a new science of human nature.

     James H. Fowler, Darren Schreiber
     Science 322 (5903): 912–914 (7 November 2008)

106. Estimating Peer Effects on Health in Social Networks We recently showed that obesity can spread socially from person to person in adults (Christakis and Fowler 2007). A natural question to ask is whether or not these results generalize to a population of adolescents. Three separate teams of researchers have analyzed the National Longitudinal Study of Adolescent Health (Add Health) and shown evidence of person-to-peron spread of obesity, but they use different methods and disagree on the interpretation of their results. Here, we conduct our own analysis of the Add Health data, provide additional evidence from the Framingham Heart Study on the social spread of obesity, and use Monte Carlo simulations to test the econometric methods we use to model peer effects. The results show that the existence of peer effects in body mass is robust to several specifications in both adults and in adolescents.

     James H. Fowler, Nicholas A. Christakis
     Journal of Health Economics 27 (5): 1400–1405 (September 2008)

107. Two Genes Predict Voter Turnout Fowler, Baker, and Dawes (2008) recently showed in two independent studies of twins that voter turnout has very high heritability. Here we investigate two specific genes that may contribute to this heritability via their impact on neurochemical processes that influence social behavior. Using data from the National Longitudinal Study of Adolescent Health, we show that a polymorphism of the MAOA gene significantly increases the likelihood of voting. We also find evidence of a gene-environment interaction between religious attendance and a polymorphism of the 5HTT gene that significantly increases voter turnout. These are the first results to ever link specific genes to political behavior and they suggest that political scientists should take seriously the claim that at least some variation in political behavior is due to innate predispositions.

     James H. Fowler, Christopher T. Dawes
     Journal of Politics 70 (3): 579–594 (July 2008)
     • New York Times Magazine 2008 Year in Ideas
     • CNN
     • Science
     • New Scientist
     • New York Times editorial
     • Presentation Slides
     • Ternary Plot R Code

108. The Colbert Bump in Campaign Donations: More Truthful Than Truthy Stephen Colbert, the host of Comedy Central's The Colbert Report, claims that politicians who appear on his show will become more popular and are more likely to win elections. Although online discussions cite anecdotal evidence in support of his claim, it has never been scrutinized scientifically. In this article I use "facts" (sorry, Stephen) provided by the Federal Election Commission to create a matched control group of candidates who have never appeared on The Colbert Report. I then compare the personal campaign donations they receive to those received by candidates who have appeared on the program's segment "Better Know a District." The results show that Democratic candidates who appear on the Report receive a statistically significant "Colbert bump" in campaign donations, raising 44% more money in a 30-day period after appearing on the show. However, there is no evidence of a similar boost for Republicans. These results constitute the first scientific evidence of Stephen Colbert's influence on political campaigns.

     James H. Fowler
     PS: Political Science & Politics, 41 (3): 533–539 (July 2008)
     • The Colbert Report
     • My op-ed on Colbert in the Los Angeles Times
     • US News and World Report
     • NPR's Story of the Day

109. The Collective Dynamics of Smoking in a Large Social Network Background
     The prevalence of smoking has decreased substantially in the United States over the past 30 years. We examined the extent of the person-to-person spread of smoking behavior and the extent to which groups of widely connected people quit together.
     Methods
     We studied a densely interconnected social network of 12,067 people assessed repeatedly from 1971 to 2003 as part of the Framingham Heart Study. We used network analytic methods and longitudinal statistical models.
     Results
     Discernible clusters of smokers and nonsmokers were present in the network, and the clusters extended to three degrees of separation. Despite the decrease in smoking in the overall population, the size of the clusters of smokers remained the same across time, suggesting that whole groups of people were quitting in concert. Smokers were also progressively found in the periphery of the social network. Smoking cessation by a spouse decreased a person's chances of smoking by 67% (95% confidence interval [CI], 59 to 73). Smoking cessation by a sibling decreased the chances by 25% (95% CI, 14 to 35). Smoking cessation by a friend decreased the chances by 36% (95% CI, 12 to 55 ). Among persons working in small firms, smoking cessation by a coworker decreased the chances by 34% (95% CI, 5 to 56). Friends with more education influenced one another more than those with less education. These effects were not seen among neighbors in the immediate geographic area.
     Conclusions
     Network phenomena appear to be relevant to smoking cessation. Smoking behavior spreads through close and distant social ties, groups of interconnected people stop smoking in concert, and smokers are increasingly marginalized socially. These findings have implications for clinical and public health interventions to reduce and prevent smoking.

     Nicholas A. Christakis, James H. Fowler
     New England Journal of Medicine 358 (21): 2249–58 (22 May 2008)
     • Supplementary Information
     • Movie of the network at NEJM
     • The original movie
     • High-resolution network image of smoking in 2001
     • High-resolution network image of smoking in 1971
     • Editorial by Steven Schroeder
     • New York Times
     • Washington Post
     • NPR Morning Edition
     • Letter from American Lung Association to New York Times
     • UCSD Press Release

110. Genetic Variation in Political Participation The decision to vote has puzzled scholars for decades. Theoretical models predict little or no variation in participation in large population elections and empirical models have typically explained only a relatively small portion of individual-level variance in turnout behavior. However, these models have not considered the hypothesis that part of the variation in voting behavior can be attributed to genetic effects. Matching public voter turnout records in Los Angeles to a twin registry, we study the heritability of political behavior in monozygotic and dizygotic twins. The results show that genes account for a significant proportion of the variation in voter turnout. We also replicate these results with data from the National Longitudinal Study of Adolescent Health and show that they extend to a broad class of acts of political participation. These are the first findings to suggest that humans exhibit genetic variation in their tendency to participate in political activities.

     James H. Fowler, Laura A. Baker, Christopher T. Dawes
     American Political Science Review 102 (2): 233–248 (May 2008)
     • New York Times Magazine 2008 Year in Ideas
     • Featured in Science

111. On the Evolutionary Origin of Prospect Theory Preferences Prospect theory scholars have identified important human decision-making biases, but they have been conspicuously silent on the question of the origin of these biases. Here we create a model that shows preferences consistent with prospect theory may have an origin in evolutionary psychology. Specifically, we derive a model from risk-sensitive optimal foraging theory to generate an explanation for the origin and function of context-dependent risk aversion and risk seeking behavior. Although this model suggests that human cognitive architecture evolved to solve particular adaptive problems related to finding sufficient food resources to survive, we argue that this same architecture persists and is utilized in other survival-related decisions that are critical to understanding political outcomes. In particular, we identify important departures from standard results when we incorporate prospect theory into theories of spatial voting and legislator behavior, international bargaining and conflict, and economic development and reform.

     Rose McDermott, James H. Fowler, Oleg Smirnov
     Journal of Politics 70 (2): 335–350 (April 2008)

112. Heritability of Cooperative Behavior in the Trust Game Although laboratory experiments document cooperative behavior in humans, little is known about the extent to which individual differences in cooperativeness result from genetic and environmental variation. In this article we report the results of two independently conceived and executed studies of monozygotic and dizygotic twins, one in Sweden, and one in the United States. The results from these studies suggest that humans are endowed with genetic variation that influences the decision to invest--and to reciprocate investment--in the classic trust game. Based on these findings, we urge social scientists to take seriously the idea that differences in peer and parental socialization are not the only forces that influence variation in cooperative behavior.

     David Cesarini, Christopher T. Dawes, James H. Fowler, Magnus Johannesson, Paul Lichtenstein, Björn Wallace
     PNAS 105 (10): 3721–3726 (11 March 2008)
     • Supporting Information
     • Ternary Plot R Code

113. Community Structure in Congressional Cosponsorship Networks We study the United States Congress by constructing networks between Members of Congress based on the legislation that they cosponsor. Using the concept of modularity, we identify the community structure of Congressmen, as connected via sponsorship/cosponsorship of the same legislation, to investigate the collaborative communities of legislators in both chambers of Congress. This analysis yields an explicit and conceptually clear measure of political polarization, demonstrating a sharp increase in partisan polarization which preceded and then culminated in the 104th Congress (1995–1996), when Republicans took control of both chambers. Although polarization has since waned in the U.S. Senate, it remains at historically high levels in the House of Representatives.

     Yan Zhang, A.J. Friend, Amanda L. Traud, Mason A. Porter, James H. Fowler, Peter J. Mucha
     Physica A 387 (7): 1705–1712 (1 March 2008)

114. A Tournament of Party Decision Rules In the spirit of Axelrod's famous series of tournaments for strategies in the repeat-play prisoner'ss dilemma, we conducted a "tournament of party decision rules" in a dynamic agent-based spatial model of party competition. A call was issued for researchers to submit rules for selecting party positions in a two-dimensional policy space. Each submitted rule was pitted against all others in a suite of very long-running simulations in which all parties falling below a declared support threshold for two consecutive elections "died" and one new party was "born" each election at a random spatial location, using a rule randomly drawn from the set submitted. The policy-selection rule most successful at winning votes over the very long run was declared the "winner". The most successful rule was identified unambiguously and combined a number of striking features. It satisficed rather than maximized in the short run; it was "parasitic" on choices made by other successful rules; and it was hard-wired not to attack other agents using the same rule, which it identified using a "secret handshake". We followed up the tournament with a second suite of simulations in a more evolutionary setting in which the selection probability of a rule was a function of its "fitness", measured in terms of the previous success of agents using the same rule. In this setting, the rule that won the original tournament pulled even further ahead of the competition. Treated as a discovery tool, tournament results raise a series of intriguing issues for those involved in the modeling of party competition.

     James H. Fowler, Michael Laver
     Journal of Conflict Resolution 52 (1): 68–92 (February 2008)
     • Online Appendix
     • Rules for the $1000 Tournament of Party Strategies

115. The Authority of Supreme Court Precedent We construct the complete network of 30,288 majority opinions written by the U.S. Supreme Court and the cases they cite from 1754 to 2002 in the United States Reports. Data from this network demonstrates quantitatively the evolution of the norm of stare decisis in the 19th Century and a significant deviation from this norm by the activist Warren court. We further describe a method for creating authority scores using the network data to identify the most important Court precedents. This method yields rankings that conform closely to evaluations by legal experts, and even predicts which cases they will identify as important in the future. An analysis of these scores over time allows us to test several hypotheses about the rise and fall of precedent. We show that reversed cases tend to be much more important than other decisions, and the cases that overrule them quickly become and remain even more important as the reversed decisions decline. We also show that the Court is careful to ground overruling decisions in past precedent, and the care it exercises is increasing in the importance of the decision that is overruled. finally, authority scores corroborate qualitative assessments of which issues and cases the Court prioritizes and how these change over time.

     James H. Fowler, Sangick Jeon
     Social Networks 30 (1): 16–30 (January 2008)
     • The Economist
     • Supreme Court data

116. Social Networks in Political Science: Hiring and Placement of PhDs, 1960–2002 Drawing on recent methodological advances, we examine the social network of political science department placements. This network permits us to estimate simultaneously 1) how well departments place their own students and 2) how effective they are in hiring students from other institutions. Using data collected by Masuoka, Grofman and Feld (2006a, b) on U.S. Ph.D. granting institutions, we provide visualizations of the connectivity among 132 departments as a social network graph in which core and periphery departments can be identified. We also show how this network has changed over time. The new social network measures conform closely to qualitative expert rankings and show that a department's placement record contributes more to its prestige than a department's ability to hire and retain faculty from core institutions.

     James H. Fowler, Bernard N. Grofman, Natalie Masuoka
     PS: Political Science & Politics 40 (4): 729–739 (October 2007)

117. Does Self-Citation Pay? Self-citations - those where authors cite their own work - account for a significant portion of all citations. These self-references may result from the cumulative nature of individual research, the need for personal gratification, or the value of self-citation as a rhetorical and tactical tool in the struggle for visibility and scientific authority. In this article we examine the incentives that underlie self-citation by studying how authors' references to their own works affect the citations they receive from others. We report the results of a macro study of more than half a million citations to articles by Norwegian scientists that appeared in the Science Citation Index. We show that the more one cites oneself the more one is cited by other scholars. Controlling for numerous sources of variation in cumulative citations from others, our models suggest that each additional self-citation increases the number of citations from others by about one after one year, and by about three after five years. Moreover, there is no significant penalty for the most frequent self-citers the effect of self-citation remains positive even for very high rates of self-citation. These results carry important policy implications for the use of citations to evaluate performance and distribute resources in science and they represent new information on the role and impact of self-citations in scientific communication.

     James H. Fowler, Dag W. Aksnes
     Scientometrics 72 (3): 427–437 (September 2007)
     • Nature News

118. Beyond the Self: Social Identity, Altruism, and Political Participation Scholars have recently extended the traditional calculus of participation model by adding a term for benefits to others. We advance this work by distinguishing theoretically a concern for others in general (altruism) from a concern for others in certain groups (social identification). We posit that both concerns generate increased benefits from participation. To test these theories, we use allocations in dictator games towards an unidentified anonymous recipient and two recipients identified only as a registered Democrat or a registered Republican. These allocations permit a distinction between altruism and social identification. The results show that both altruism and social identification significantly increase political participation. The results also demonstrate the usefulness of incorporating benefits that stem from sources beyond material self-interest into rational choice models of participation.

     James H. Fowler, Cindy D. Kam
     Journal of Politics 69 (3): 813–827 (August 2007)
     • Web appendix

119. The Spread of Obesity in a Large Social Network Over 32 Years Background
     The prevalence of obesity has increased substantially over the past 30 years. We performed a quantitative analysis of the nature and extent of the person-to-person spread of obesity as a possible factor contributing to the obesity epidemic.
     Methods
     We evaluated a densely interconnected social network of 12,067 people assessed repeatedly from 1971 to 2003 as part of the Framingham Heart Study. The body-mass index was available for all subjects. We used longitudinal statistical models to examine whether weight gain in one person was associated with weight gain in his or her friends, siblings, spouse, and neighbors.
     Results
     Discernible clusters of obese persons were present in the network at all time points, and the clusters extended to three degrees of separation. These clusters did not appear to be solely attributable to the selective formation of social ties among obese persons. A person's chances of becoming obese increased by 57% (95% confidence interval [CI], 6 to 123) if he or she had a friend who became obese in a given interval. Among pairs of adult siblings, if one sibling became obese, the chance that the other would become obese increased by 40% (95% CI, 21 to 60). If one spouse became obese, the likelihood that the other spouse would become obese increased by 37% (95% CI, 7 to 73). These effects were not seen among neighbors in the immediate geographic location. Persons of the same sex had relatively greater influence on each other as compared with those of the opposite sex. The spread of smoking cessation did not account for the spread of obesity in the network.
     Conclusions
     Network phenomena appear to be relevant to the biologic and behavioral trait of obesity, and obesity appears to spread through social ties. These findings have implications for clinical and public health interventions.

     Nicholas A. Christakis, James H. Fowler
     New England Journal of Medicine 357 (4): 370–379 (26 July 2007)
     • Supplementary Information
     • See a movie of the network at NEJM
     • Here's the original movie
     • High-resolution network image of obesity in 2000
     • Editorial by Albert-László Barabási
     • Correspondence about the article in NEJM, 1 Nov 2007
     • New York Times front page
     • New York Times Week in Review
     • 30 minute TV program about the study on Health Matters
     • UCSD Press Release

120. Network Analysis and the Law: Measuring the Legal Importance of Supreme Court Precedents We construct the complete network of 26,681 majority opinions written by the U.S. Supreme Court and the cases that cite them from 1791 to 2005. We describe a method for using the patterns in citations within and across cases to create importance scores that identify the most legally relevant precedents in the network of Supreme Court law at any given point in time. Our measures are superior to existing network-based alternatives and, for example, offer information regarding case importance not evident in simple citation counts. We also demonstrate the validity of our measures by showing that they are strongly correlated with the future citation behavior of state courts, the U.S. Courts of Appeals, and the U.S. Supreme Court. In so doing, we show that network analysis is a viable way of measuring how central a case is to law at the Court and suggest that it can be used to measure other legal concepts.

     James H. Fowler, Timothy R. Johnson, James F. Spriggs II, Sangick Jeon, Paul J. Wahlbeck
     Political Analysis, 15 (3): 324–346 (July 2007)

121. Egalitarian Motives in Humans Participants in laboratory games are often willing to alter others' incomes at a cost to themselves and this behaviour has the effect of promoting cooperation. What motivates this action is unclear: punishment and reward aimed at promoting cooperation cannot be distinguished from attempts to produce equality. To understand costly taking and costly giving, we create an experimental game that isolates egalitarian motives. The results show that subjects reduce and augment others' incomes, at a personal cost, even when there is no cooperative behaviour to be reinforced. Furthermore, the size and frequency of income alterations are strongly influenced by inequality. Emotions towards top earners become increasingly negative as inequality increases, and those who express these emotions spend more to reduce above-average earners' incomes and to increase below-average earners' incomes. The results suggest that egalitarian motives affect income altering behaviours, and may thus be an important factor underlying the evolution of strong reciprocity and, hence, cooperation in humans

     Christopher T. Dawes, James H. Fowler, Tim Johnson, Richard McElreath, Oleg Smirnov
     Nature 446: 794–796 (12 April 2007)
     • Supplementary Information
     • Reuters
     • UCSD Press Release

122. Policy-Motivated Parties in Dynamic Political Competition We analyze a model of a dynamic political competition between two policy-motivated parties under uncertainty. The model suggests that electoral mandates matter: increasing the margin of victory in the previous election causes both parties to shift towards policies preferred by the winner, and the loser typically shifts more than the winner. The model also provides potential answers to a number of empirical puzzles in the field of electoral politics. In particular, we provide possible explanations for why close elections may lead to extreme platforms by both parties,why increased extremism in the platform of one party may lead to greater moderation in the platform of the other party,and why increasing polarization of the electorate causes winning candidates to become more sensitive to mandates. We also show that, contrary to previous findings, increasing uncertainty sometimes decreases platform divergence. finally, we pay special attention to the proper methodology for doing numerical comparative statics analysis in computational models.

     Oleg Smirnov, James H. Fowler
     Journal of Theoretical Politics 19 (1): 9–31 (January 2007)

123. Mandates, Parties, and Voters: How Elections Shape the Future Most research on two-party elections has considered the outcome as a single, dichotomous event: either one or the other party wins. In this book, the authors investigate not just who wins, but by how much, and they marshal compelling evidence that mandates--in the form of margin of victory--matter. Using theoretical models, computer simulation, carefully designed experiments, and empirical data, the authors show that after an election the policy positions of both parties move in the direction preferred by the winning party--and they move even more if the victory is large. (book)

     James H. Fowler, Oleg Smirnov
     Temple University Press (2007)
     • Includes the chapters A Dynamic Calculus of Voting and Party Responsiveness and Mandate Balancing
     • Review in Perspectives by André Blais
     • Review in Political Science Quarterly by Scott McClurg

124. The Southern California Twin Register at the University of Southern California: II The Southern California Twin Register was initiated in 1984 at the University of Southern California, and continues to grow. This article provides an update of the register since it was described in the 2002 special issue of this journal. The register has expanded considerably in the past 4 years, primarily as a result of recent access to Los Angeles County birth records and voter registration databases. Currently, this register contains nearly 5000 twin pairs, the majority of whom are school age. The potential for further expansion in adult twins using voter registration records is also described. Using the Los Angeles County voter registration database, we can identify a large group of individuals with a high probability of having a twin who also resides in Los Angeles County. In addition to describing the expansion of register, this article provides an overview of an ongoing investigation of 605 twin pairs who are participating in a longitudinal study of behavioral problems during childhood and adolescence. Characteristics of the twins and their families are presented, indicating baseline rates of conduct problems, depression and anxiety disorders, and attention-deficit/hyperactivity disorder diagnoses which are comparable to nontwins in this age range.

     Laura A. Baker, Mafalda Barton, Adrian Raine, James H. Fowler
     Twin Research and Human Genetics 9 (6): 933–940 (December 2006)

125. Connecting the Congress: A Study of Cosponsorship Networks Using large-scale network analysis I map the cosponsorship networks of all 280,000 pieces of legislation proposed in the U.S. House and Senate from 1973 to 2004. In these networks, a directional link can be drawn from each cosponsor of a piece of legislation to its sponsor. I use a number of statistics to describe these networks such as the quantity of legislation sponsored and cosponsored by each legislator, the number of legislators cosponsoring each piece of legislation, the total number of legislators who have cosponsored bills written by a given legislator, and network measures of closeness, betweenness, and eigenvector centrality. I then introduce a new measure I call "connectedness" which uses information about the frequency of cosponsorship and the number of cosponsors on each bill to make inferences about the social distance between legislators. Connectedness predicts which members will pass more amendments on the floor, a measure that is commonly used as a proxy for legislative influence. It also predicts roll call vote choice even after controlling for ideology and partisanship.

     James H. Fowler
     Political Analysis 14 (4): 456–487 (Fall 2006)
     • Washington Post
     • Cosponsorship network data

126. Legislative Cosponsorship Networks in the U.S. House and Senate In the US House and Senate, each piece of legislation is sponsored by a unique legislator. In addition, legislators can publicly express support for a piece of legislation by cosponsoring it. The network of sponsors and cosponsors provides information about the underlying social networks among legislators. I use a number of statistics to describe the cosponsorship network in order to show that it behaves much differently than other large social networks that have been recently studied. In particular, the cosponsorship network is much denser than other networks and aggregate features of the network appear to be influenced by institutional arrangements and strategic incentives. I also demonstrate that a weighted closeness centrality measure that I call "connectedness" can be used to identify influential legislators.

     James H. Fowler
     Social Networks 28 (4): 454–465 (October 2006)
     • Washington Post
     • Cosponsorship network data

127. Altruism and Turnout Scholars have recently reworked the traditional calculus of voting model by adding a term for benefits to others. Although the probability that a single vote affects the outcome of an election is quite small, the number of people who enjoy the benefit when the preferred alternative wins is large. As a result, people who care about benefits to others and who think one of the alternatives makes others better offare more likely to vote.I test the altruism theory ofvoting in the laboratory by using allocations in a dictator game to reveal the degree to which each subject is concerned about the well-being of others. The main findings suggest that variation in concern for the well-being of others in conjunction with strength of party identification is a significant factor in individual turnout decisions in real world elections. Partisan altruists are much more likely to vote than their nonpartisan or egoist peers.

     James H. Fowler
     Journal of Politics 68 (3): 674–683 (August 2006)
     • Web appendix
     • Chronicle of Higher Education

128. Patience as a Political Virtue: Delayed Gratification and Turnout A number of scholars have demonstrated that voter turnout is influenced by the costs of processing information and going to the polls, and the policy benefits associated with the outcome of the election. However, no one has yet noted that the costs of voting are paid on or before Election Day, while policy benefits may not materialize until several days, months, or even years later. Since the costs of voting must be borne before the benefits are realized, people who are more patient should be more willing to vote. We use a "choice game" from experimental economics to estimate individual discount factors which are used to measure patience. We then show that patience significantly increases voter turnout.

     James H. Fowler, Cindy D. Kam
     Political Behavior 28 (2): 113–128 (June 2006)

129. Habitual Voting and Behavioral Turnout Bendor, Diermeier, and Ting (2003) develop a behavioral alternative to rational choice models of turnout. However, the assumption they make about the way individuals adjust their probability of voting biases their model towards their main result of significant turnout in large populations. Moreover, the assumption causes individuals to engage in casual voting (sometimes people vote and sometimes they abstain). This result is at odds with a substantial literature that indicates most people engage in habitual voting (they either always vote or always abstain). I develop an alternative model to show how feedback in the probability adjustment mechanism affects the behavioral model. The version of this model without feedback yields both high turnout and habitual voting.

     James H. Fowler
     Journal of Politics 68 (2): 335–344 (May 2006)
     • Web appendix

130. Elections and Markets: The Effect of Partisan Orientation, Policy Risk, and Mandates on the Economy Rational partisan theory's exclusive focus on electoral uncertainty ignores the importance of policy uncertainty for the economy. I develop a theory of policy risk to account for this uncertainty. Using an innovative measure of electoral probabilities based on Iowa Electronic Markets futures data for the United States from 1988 to 2000, I test both theories. As predicted by rational partisan theory, positive changes in the probability that the Left wins the Presidency or the Congress lead to increases in nominal interest rates, implying that expectations of inflation have increased. As predicted by the policy risk theory, positive changes in the electoral probability of incumbent governments and divided governments lead to significant declines in interest rates, implying that expectations of inflation risk have decreased. And as an extension to both theories, I find that electoral margins matter for the economy--partisan and policy risk effects depend not only on which party controls the government, but how large its margin of victory is.

     James H. Fowler
     Journal of Politics 68 (1): 89–103 (February 2006)
     • Web appendix

131. Second Order Free Riding Problem Solved? Panchanathan and Boyd describe a model of indirect reciprocity in which mutual aid among cooperators can promote large-scale human cooperation without succumbing to a second-order free-riding problem (whereby individuals receive but do not give aid). However, the model does not include second-order free riders as one of the possible behavioural types. Here I present a simplified version of their model to demonstrate how cooperation unravels if second-round defectors enter the population, and this shows that the free-riding problem remains unsolved.

     James H. Fowler
     Nature 437; doi:10.1038/nature04201 (22 September 2005)

132. Altruistic Punishment and the Origin of Cooperation How did human cooperation evolve? Recent evidence shows that many people are willing to engage in altruistic punishment, voluntarily paying a cost to punish noncooperators. Although this behavior helps to explain how cooperation can persist, it creates an important puzzle. If altruistic punishment provides benefits to nonpunishers and is costly to punishers, then how could it evolve? Drawing on recent insights from voluntary public goods games, I present a simple evolutionary model in which altruistic punishers can enter and will always come to dominate a population of contributors, defectors, and nonparticipants. The model suggests that the cycle of strategies in voluntary public goods games does not persist in the presence of punishment strategies. It also suggests that punishment can only enforce payoff-improving strategies, contrary to a widely cited "folk theorem" result that suggests that punishment can allow the evolution of any strategy.

     James H. Fowler
     PNAS 102 (19): 7047–7049 (10 May 2005)
     • U.S. News and World Report

133. Dynamic Responsiveness in the US Senate I develop a theory of dynamic responsiveness that suggests that parties that win elections choose candidates who are more extreme and parties that lose elections choose candidates who are more moderate. Moreover, the size of past victories matters. Close elections yield little change, but landslides yield larger changes in the candidates offered by both parties. I test this theory by analyzing the relationship between Republican vote share in U.S. Senate elections and the ideology of candidates offered in the subsequent election. The results show that Republican (Democratic) victories in past elections yield candidates who are more (less) conservative in subsequent elections, and the effect is proportional to the margin of victory. This suggests that parties or candidates pay attention to past election returns. One major implication is that parties may remain polarized in spite of their responsiveness to the median voter.

     James Fowler
     American Journal of Political Science 49 (2): 299–312 (April 2005)

134. Egalitarian Motive and Altruistic Punishment Altruistic punishment is a behaviour in which individuals punish others at a cost to themselves in order to provide a public good. Fehr and Gachter present experimental evidence suggesting that negative emotions toward non-cooperators motivate punishment which, in turn, facilitates high levels of cooperation in humans. Using Fehr and Gachter's original data, we provide an alternative analysis of the experiment that suggests egalitarian motives are more important than motives to punish non-cooperative behaviour--a finding consistent with evidence that humans may have an evolutionary incentive to punish the highest earners in order to promote equality, not cooperation.

     James H. Fowler, Tim Johnson, Oleg Smirnov
     Nature 433; doi:10.1038/nature03256 (06 January 2005)

135. Dynamic Parties and Social Turnout: An Agent-Based Model The authors develop an agent-based model of dynamic parties with social turnout built upon developments in different fields within social science. This model yields significant turnout, divergent platforms, and numerous results consistent with the rational calculus of voting model and the empirical literature on social turnout. In a simplified version of the model, the authors show how a local imitation structure inherently yields dynamics that encourage positive turnout. The model also generates new hypotheses about the importance of social networks and citizen-party interactions.

     James H. Fowler, Oleg Smirnov
     American Journal of Sociology 110 (4): 1070–1094 (January 2005)

136. Turnout in a Small World This chapter investigates between-voter interactions in a social network model of turnout. It shows that if 1) there is a small probability that voters imitate the behavior of one of their acquaintances, and 2) individuals are closely connected to others in a population (the "small-world" effect), then a single voting decision may affect dozens of other voters in a "turnout cascade." If people tend to be ideologically similar to other people they are connected to, then these turnout cascades will produce net favorable results for their favorite candidate. By changing more than one vote with one's own turnout decision, the turnout incentive is thus substantially larger than previously thought. We analyze conditions that are favorable to turnout cascades and show that the effect is consistent with real social network data from Huckfeldt and Sprague's South Bend and Indianapolis-St. Louis election surveys. We also suggest that turnout cascades may help explain over-reporting of turnout and the ubiquitous belief in a duty to vote.

     James H. Fowler
     in The Social Logic of Politics: Personal Networks as Contexts for Political Behavior, ed. Alan Zuckerman,Temple University Press, 269–287 (2005)

137. The United States and South Korean Democratization In 1987 South Korea initiated a successful transition to democracy, while previous attempts in 1979 and 1980 failed. This paper distinguishes two cycles of liberalization in South Korea and then develops a conceptual understanding that is used to test two common schools of thought. One school asserts that the United States had little impact on democratization in Korea and that domestic factors explain the delayed transition. The other school implies that the U.S. could have improved prospects for democratization by not approving Chun Doo Hwan's request to use Combined Forces Command troops to repress demonstrations in 1980. finding both sets of explanations unsatisfactory, this paper draws on recently declassified documents and interviews with State Department officials to advance the hypothesis that it was U.S. public pressure which played a critical role in determining the timing of South Korea's transition to democracy. finally, the use of public pressure is found to have been greatly affected by unrelated foreign policy crises in Iran and the Philippines, illuminating the process whereby conflicts in other countries that had no direct bearing on South Korea ultimately affected the outcome of its own domestic political process.

     James Fowler
     Political Science Quarterly 114 (2): 265–288 (Summer 1999)
     • Also appears in The New American Interventionism: Lessons from Successes and Failures, ed. Demetrios Caraley, Columbia University Press (2000)

SOFTWARE AND DATA

• Code to create fancy ternary plots with 95% credible intervals.
• Dataverse repository
• Replication code and data for Cooperative Behavior Cascades in Human Social Networks
• Supreme Court Citation Network Data used for The Authority of Supreme Court Precedent
• Cosponsorship Data used for Connecting the Congress: A Study of Cosponsorship Networks and Legislative Cosponsorship Networks in the U.S. House and Senate
• R program for testbed including all submitted strategies in the $1000 Tournament of Party Strategies
• R program for pre-tournament testbed of the $1000 Tournament of Party Strategies
• Data for the public goods game and random income game analyzed in The Behavioral Logic of Collective Action: Partisans Cooperate and Punish More Than Non-Partisans
• R program for Dynamic Parties and Social Turnout
• R program for Habitual Voting and Behavioral Turnout
• Agent-based model and simulation data (Stata format) for Turnout in a Small World
• NES data (Stata format) for A Dynamic Calculus of Voting

TEACHING

University of California, San Diego

• POLI 100F: Social Networks
• POLI 279: Topics in Methodology: Social Networks
  Powerpoints: #1 #2 #3 #4
• CAT 3: The New (Old) Connectivity (PDF)
• INTL 190H: Honors Seminar in International Studies
• POLI 191A: Honors Seminar in Political Science
  • Memos #2, #3, #4
• POLI 102G: Politics, Puzzles, and Games

EITM Summer Institute, Duke University

• Day 1 powerpoint slides
• Day 2 powerpoint slides
• Day 3 powerpoint slides

EITM Summer Institute, UCLA

• Day 1 powerpoint slides
• Day 2 powerpoint slides
• Day 3 part 1 powerpoint slides
• Day 3 part 2 beamer slides

University of California, Davis

• Scientific Study of Politics - pdf file of lecture slides is here
• Strategy of Politics
• Introduction to Modeling Politics
• Advanced Formal Models
• Research Methods Seminar: Game Theory
• Democratic Theory

Harvard University

• Math (P)refresher for Political Scientists (Lecturer)
• Strategy of International Politics (Head TF)
• Thinking about Politics: A Rational Choice Approach (TF)
• Sophomore Tutorial: Constitutional Democracy in America (TF)
• The Modern World Economy, 1873-2000 (TF)
• Growth and Development in Historical Perspective (TF)

Yale University

• Strategy, Technology, and War (TF)
• The United Nations and World Order (TF)

United States Peace Corps, Latacunga, Ecuador

• Health Promotion Educator (1992-1994). Educated 25 community health promoters. Taught health lessons to adults and children in 40 indigenous communities. Designed and budgeted gravity flow water systems for 10,000 people in 30 communities. Supervised construction of 900+ latrines for 5,000 people in 9 rural communities. Learned fluent Spanish and rudimentary Quichua.
• English conversation (1993-1994). Universidad Técnica de Ambato and Instituto Técnico Superior del Ejército.

This work by James H. Fowler is licensed under a
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