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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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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?

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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 human! s. 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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

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 Fowler

James Fowler is Professor of Medical Genetics and Political Science at the University of California, San Diego. His work lies at the intersection of the natural and social sciences, with a focus on social networks, behavioral science, evolution, politics, genetics, and big data. His CV is here.

James was recently named a Fellow of the John Simon Guggenheim Foundation, one of Foreign Policy's Top 100 Global Thinkers, TechCrunch's Most Innovative People in Democracy, and Most Original Thinker of the year by The McLaughlin Group. He has also been on The Colbert Report.

James's research on genopolitics with Chris Dawes has been featured in New York Times Magazine's Year in Ideas. His work on overconfidence with Dom Johnson has been featured in Discover Magazine's Year in Science. And his research on social networks with Nicholas Christakis has been featured in Time's Year in Medicine (twice), and in Harvard Business Review's Breakthrough Business Ideas.

Science magazine dubbed Christakis and Fowler the "dynamic duo" (though James thinks Nicholas makes a better Adam West). Together they have written a book on social networks for a general audience called Connected. Winner of a Books for a Better Life Award, it has been translated into twenty languages, named an Editor's Choice by the New York Times Book Review, and featured in Wired, Oprah's Reading Guide, Business Week's Best Books of the Year, GOOD's 15 Books You Must Read, and a cover story in New York Times Magazine.

 

CONVERSATIONS

 

PUBLICATIONS

  1. 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 (February 2013)

  2. Widower 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 (forthcoming)

  3. 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): TBD (May 2013)

  4. 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 (forthcoming)

  5. 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 (forthcoming)

  6. 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)

  7. 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)

  8. 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)

  9. 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)

  10. 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 (February 2013)

  11. 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)

  12. 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 (January 2013)

  13. 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)

  14. 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)

  15. 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)

  16. 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)

  17. 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.

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

  18. 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)

  19. 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)

  20. 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)

  21. 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)

  22. 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 Apicella, Frank W. Marlowe, James H. Fowler, Nicholas A. Christakis
    Nature 477: 497–501 (26 January 2012)

  23. 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)

  24. 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)

  25. 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)

  26. 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)

  27. 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)

  28. 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

  29. 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)

  30. 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)

  31. 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)

  32. 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)

  33. 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 (September 2010)

  34. 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)

  35. 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)

  36. 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)

  37. 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 (March 2010)

  38. 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)

  39. 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)

  40. 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)

  41. 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)

  42. 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)

  43. 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)

  44. 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)

  45. 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)

  46. 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)

  47. 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)

  48. 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)

  49. 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)

  50. 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)

  51. 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)

  52. 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)

  53. 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)

  54. 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)

  55. 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)

  56. 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)

  57. 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)

  58. 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)

  59. 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)

  60. 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)

  61. 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)

  62. 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)

  63. 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)

  64. 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)

  65. 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)

  66. 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)

  67. 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)

  68. 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)

  69. 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)

  70. 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)

  71. 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)

  72. 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)

  73. 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)

  74. 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)

  75. 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)

  76. 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)

  77. 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)

  78. 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)

  79. 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)

  80. 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)

SOFTWARE AND DATA


TEACHING

University of California, San Diego

EITM Summer Institute, Duke University

EITM Summer Institute, UCLA

University of California, Davis

Harvard University

Yale University

United States Peace Corps, Latacunga, Ecuador

 

 

 


This work by James H. Fowler is licensed under a
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