Social selection and peer influence in an online social network

Abstract

Disentangling the effects of selection and influence is one of social science's greatest unsolved puzzles: Do people befriend others who are similar to them, or do they become more similar to their friends over time? Recent advances in stochastic actor-based modeling, combined with self-reported data on a popular online social network site, allow us to address this question with a greater degree of precision than has heretofore been possible. Using data on the Facebook activity of a cohort of college students over 4 years, we find that students who share certain tastes in music and in movies, but not in books, are significantly likely to befriend one another. Meanwhile, we find little evidence for the diffusion of tastes among Facebook friends-except for tastes in classical/jazz music. These findings shed light on the mechanisms responsible for observed network homogeneity; provide a statistically rigorous assessment of the coevolution of cultural tastes and social relationships; and suggest important qualifications to our understanding of both homophily and contagion as generic social processes.

Fig. 1.

Visualization of the distribution of students’ music preferences on Facebook, featuring all items that appeared among the 100 most popular music tastes in at least one wave of data (n = 145). Similar tastes appear closer together in 3D space, where similarity is defined as the rate of co-occurrence between two tastes, and coordinates are determined by multidimensional scaling. Node size is proportionate to taste popularity, and colors refer to the five largest clusters of tastes identified by a hierarchical clustering algorithm. Cluster names are generalizations for illustrative purposes only. Visualizations for movies and books are provided in the Supporting Information, as well as animations of all three “taste spaces” for closer inspection.

Fig. 2.

Parameter estimates β and 95% confidence intervals for a stochastic actor-based model of the evolution of Facebook friendships over 4 years (n = 1,001). Significant coefficients are labeled with an asterisk, where a coefficient is considered significant if the 95% confidence interval does not contain β = 0. Coefficients generally correspond to the change in log-odds of a tie being present vs. absent if the given criterion is met (e.g., the friendship is between two friends-of-friends or two students who share the same gender), although the case for socioeconomic homophily—a continuous variable—is more complex (SI Materials and Methods, Evolution of Facebook Friendships).

Fig. 3.

Parameter estimates β and 95% confidence intervals for selection and influence effects from 15 models of the coevolution of friendships and tastes (n = 211 for music, n = 201 for movies, n = 191 for books). Significant coefficients are labeled with an asterisk, where a coefficient is considered significant if the 95% confidence interval does not contain β = 0. Selection effects measure the tendency for a tie to develop between two students who both express tastes in the given cluster; influence effects measure the tendency for students whose friends express tastes in the given cluster to themselves adopt tastes in that cluster (SI Materials and Methods, Coevolution of Tastes and Friendships).