Jaime E. Settle

A 61-Million-Person Experiment in Social Influence and Political Mobilization

Human behaviour is thought to spread through 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 US 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 also the users’ friends, and friends of friends. The effect of social transmission on real-world voting was greater 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.

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 nonreproductive 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 in an independent sample from the Framingham Heart Study verifies that DRD2 exhibits significant homophily and that CYP2A6 exhibits significant heterophily. These unique 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.

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).

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 or combination of variants associated with political ideology have so far been identified. Here, we hypothesize that individuals with a genetic predisposition toward 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. Among those with DRD4-7R, we find that the number of friendships a person has in adolescence is significantly associated with liberal political ideology. Among those without the gene variant, there is no association. This is the first study 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 political preferences.

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, the authors hypothesize that genes contribute to variation in a general tendency toward strength of partisanship. Using data collected at the Twins Days Festival, the authors compare the similarity of partisan strength in identical twins who share all of their genes to the similarity of partisan strength in nonidentical twins who share only half of their genes. The results show that heritability accounts for almost half of the variance in strength of partisan attachment, suggesting we should pay closer attention to the role of biology in the expression of important political behaviors.

The Social Origins of Adult Political Behavior

Political socialization research has focused on the role of parents, extracurricular activities, and the school curriculum during adolescence on shaping early adult political behavior (Beck & Jennings, 1982; Flanagan, Syvertsen, & Stout, 2007; Torney-Purta, Richardson, & Barber, 2004). However, no study to date has examined how properties of adolescents’ social networks affect the development of adult political outcomes. Using social network analysis, we find that both a respondent’s social integration in high school and his friends’ perceptions of their own social integration affect the respondent’s later political behavior as a young adult. Peer and network effects are at work in political socialization. This has important implications for our understanding of the development of social capital, political trust, and political participation, as well as our general understanding about how one’s social network influences one’s own attitudes and behavior.

Integrating social science and genetics: news from the political front.

There has been growing interest in the use of genetic models to expand the understanding of political preferences, attitudes, and behaviors. Researchers in the social sciences have begun incorporating these models and have revealed that genetic differences account for individual differences in political beliefs, behaviors, and responses to the political environment. The first Integrating Genetics and the Social Sciences Conference, held at Boulder, Colorado in May of 2010, brought together these researchers. As a result, we jointly review the last 5 years of research in this area. In doing so, we explicate the methods, findings, and limitations of behavior genetic approaches, including twin designs, association studies, and genome-wide analyses, in their application toward exploring political preferences.

Genes, psychological traits and civic engagement.

Civic engagement is a classic example of a collective action problem: while civic participation improves life in the community as a whole, it is individually costly and thus there is an incentive to free ride on the actions of others. Yet, we observe significant inter-individual variation in the degree to which people are in fact civically engaged. Early accounts reconciling the theoretical prediction with empirical reality focused either on variation in individuals’ material resources or their attitudes, but recent work has turned to genetic differences between individuals. We show an underlying genetic contribution to an index of civic engagement (0.41), as well as for the individual acts of engagement of volunteering for community or public service activities (0.33), regularly contributing to charitable causes (0.28) and voting in elections (0.27). There are closer genetic relationships between donating and the other two activities; volunteering and voting are not genetically correlated. Further, we show that most of the correlation between civic engagement and both positive emotionality and verbal IQ can be attributed to genes that affect both traits. These results enrich our understanding of the way in which genetic variation may influence the wide range of collective action problems that individuals face in modern community life.

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.

Social Endorsement Cues and Political Participation

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