Best Selling Books by James H. Fowler

Celebrated scientists Nicholas Christakis and James Fowler explain the amazing power of social networks and our profound influence on one another''s lives. Your colleague''s husband''s sister can make you fat, even if you don''t know her. A happy neighbor has more impact on your happiness than a happy spouse. These startling revelations of how much we truly influence one another are revealed in the studies of Dr. Christakis and Fowler, which have repeatedly made front-page news nationwide. In Connected, the authors explain why emotions are contagious, how health behaviors spread, why the rich get richer, even how we find and choose our partners. Intriguing and entertaining, Connected overturns the notion of the individual and provides a revolutionary paradigm-that social networks influence our ideas, emotions, health, relationships, behavior, politics, and much more. It will change the way we think about every aspect of our lives.

Previous research has indicated that higher levels of social interactions, or greater social capital, tend to create higher levels of civic engagement and social trust. We used a large, nationally representative longitudinal survey of youth to examine the relationship between social capital, as measured by reported friendships in junior high and high school, and experiences in young adulthood with various dimensions of community engagement and trust in the federal, state, and local governments. After adjustment for a number of potential confounding variables, results showed that the total number of friends students had in middle and high school was positively associated with community engagement and trust in all levels of government in young adulthood. These findings suggest that social relationships, community engagement, and trust in government are linked, and that social experiences early in life may have an enduring effect on the capacity of communities and political institutions to govern themselves.

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 subjects most interested in reducing the difference between their own well-being and the well-being of others were no more likely to.

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.

Altruism refers to a willingness to pay a personal cost to make others better off. Past research has established a link between altruism and political participation, primarily among college students. We show that dictator game behavior predicts support for humanitarian norms and donations to Hurricane Katrina victims, suggesting that dictator game allocations are valid measures of altruism. Moreover, we show that this measure of altruism predicts participation in politics, suggesting that past results with students can be generalized to a broader population. Finally, consistent with the argument that altruists only participate when they think doing so will make everyone better off, we show that there is no relationship between altruism and voter turnout in an election where the outcome is distributive and where it is not clear that either political outcome will produce a net societal gain.

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.

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 neighbors (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.

International relations and legal theories on treaty design and participation have relied heavily on the structure of bargaining problems, the allocation of power in the international system, and interest group politics to explain states'' preferences for cooperation. Using experiments drawn from behavioral economics and cognitive psychology -- along with a substantive survey focused on international trade treaties -- we suggest that the personality traits of the individual people asked to play key roles in negotiating and ratifying international treaties also shape their preferences for how treaties are designed and put into practice. Players whose personality traits include patience were more likely to seek treaties with larger numbers of countries (and thus larger long-term benefits). And players with the skill to anticipate how others will respond over multiple iterations of strategic games also were likely to imagine that the complex strategic challenges of large membership are manageable. We find that the presence of an enforcement mechanism increased the willingness of players to join treaties. However, personality traits were even more important. More strategic players also were more likely to favor joining the agreement and this effect is about twice the effect of adding enforcement. Our study, based on a sample of 509 university students, provides a baseline for future experimental and survey research on actual policy elites who design and implement treaties.

International relations theories have largely ignored the role of individual people who play key roles in treaty design and participation; instead, that scholarship assumes that other factors, such as treaty enforcement, matter most. We use experiments drawn from behavioral economics and cognitive psychology -- along with a substantive survey focused on international trade treaties -- to illustrate how two traits (patience and strategic skills) could influence treaty outcomes. More patient and strategic players favor treaties with larger numbers of countries (and thus larger long-term benefits). These behavioral traits had much larger impacts on simulated treaty outcomes than treaty enforcement mechanisms. This study is based on a sample of 509 university students yet provides a baseline for future experimental and survey research on actual policy elites who design and implement treaties; a preliminary sample of 73 policy elites displays the same main patterns described in this paper.

We 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.

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.

We construct the complete network of 28,951 majority opinions written by the U.S. Supreme Court and the cases they cite from 1792 to 2005. We illustrate some basic properties of this network and then describe a method for creating importance scores using the data to identify the most important Court precedents at any point in time. This method yields dynamic rankings that can be used to predict the future citation behavior of state courts, the U.S. Courts of Appeals, and the U.S. Supreme Court, and these rankings outperform several commonly used alternative measures of case importance.

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 distance measures for these networks. We apply our sink based distance measure and the single-linkage hierarchical clustering algorithm to the first quarter century of decisions of the United States Supreme Court. Despite applying the simplest distance measure and a straight forward clustering algorithm, qualitative analysis reveals that accurate clusterings are produced by this scheme.

We conduct experiments in which subjects participate in both a game that measures preferences for income equality and a public goods game involving costly punishment. The results indicate that individuals who care about equality are those who are most willing to punish free-riders in public goods games.

The Southern California Twin Register was initiated in 1984 at the University of Southern California, and continues to grow. This paper 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 four 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 paper 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 ADHD diagnoses which are comparable to non-twins in this age range.

The COVID-19 pandemic represents a massive global health crisis. Because the crisis requires large-scale behaviour change and places significant psychological burdens on individuals, insights from the social and behavioural sciences can be used to help align human behavior with the recommendations of epidemiologists and public health experts. Here we discuss evidence from a selection of research topics relevant to pandemics, including work on navigating threats, social and cultural influences on behaviour, science communication, moral decision-making, leadership, and stress and coping. In each section, we note the nature and quality of prior research, including uncertainty and unsettled issues. We identify several insights for effective response to the COVID-19 pandemic, and also highlight important gaps researchers should move quickly to fill in the coming weeks and months.

Background: The prevalence of obesity has increased substantially over the past 30 years. We quantitatively explored the nature and extent of person-to-person spread of obesity as a possible contributing factor explaining this increase. Methods: We developed a densely interconnected social network of 12,067 people assessed repeatedly from 1971 to 2003 as part of the Framingham Heart Study. Measured 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 friends, siblings, spouses, and neighbors. Results: Discernible clusters of obese persons were present in the network at all time points, and the clusters extended three people deep. These clusters were not solely due to selective formation of social ties among obese persons. A friend becoming obese in a given time interval increased a person''s chances of becoming obese by 57% (95% CI: 6%-123%). Among pairs of adult siblings, one becoming obese increased the chance that the other became obese by 40% (21%-60%). Among spouses, one becoming obese increased the likelihood that the other became obese by 37% (7%-73%). Immediate neighbors did not exhibit these effects. In general, same-gender persons showed relatively greater influence on each other. The spread of smoking cessation did not account for the inter-personal spread of obesity. Conclusions: Network phenomena appear relevant to the bio-behavioral trait of obesity. Obesity appears to spread across social ties, a finding with implications for clinical and public health interventions.

Altruistic punishment is a behaviour in which individuals punish others at a cost to themselves in order to provide a public good. Fehr and Gächter1 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 Gächter''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.

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 U.S. from 1988-2000, 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.

A recent model by Panchanathan and Boyd suggests that mutual aid among cooperators can promote large-scale human cooperation without succumbing to a second order free riding problem in which individuals receive aid without giving it. In a companion article, Fehr claims the model "solves [the] second order free riding problem." However, the model does not include second order free riders as one of the possible behavioural types. I present a simplified version of their model to demonstrate how cooperation unravels if second round defectors enter the population.

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. While this behaviour 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 punishment can allow the evolution of any strategy.

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.

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

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

Past research suggests that spouses influence one another to vote, but relies almost exclusively on correlation in turnout. It is therefore difficult to establish whether spouses mobilize each other or tend to marry similar others. Here, we test the 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. Variations in this "widowhood effect" on voting support a social isolation explanation for the drop in turnout.

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.

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.