| The dissertation explores multifaceted nature of peer relations in three chapters: the first chapter uses the natural experiment of randomly assigned college roommates to estimate causal influences of peers on health behaviors. Significant peer effects are found for church attendance, physical exercise, drinking and binge drinking, more importantly, the effects vary by behavioral level of the influencer. The results also show gender differences in peer influence. All findings consistently point to the mechanism that peers influence one's behavior directly by providing opportunities for individuals to engage in the activity. The second chapter extends the line of inquiry on genetic similarity among friends by taking advantages of a quasi-experiment design to test variation in genetic homophily in different social contexts and exploring whether individual choice further gives rise to differentiated genetic similarity through friendship dynamics. Using two independent studies which contain the same set of genetic markers, the study shows that (1) beyond individual genetic polymorphism, friends are more alike than random pairs based on a set of behavior related genes, (2) greater the contextual constrain on friendship choice, smaller the genetic similarity among friends and (3) individual choice may give rise to increased level of genetic homophily. The study suggests the role of genetic similarity in driving the way we pick friends, also highlights the fundamental role of broad social contexts in moderating genetic influences on complex behaviors, such as friendship. In the third chapter, a relatively understudied area of social networks involves friendship reciprocity, the study investigates the impacts of individual status, reflected by his or her centrality in a social network, on the likelihood of friendship reciprocity between individuals. The study applies both random effect model and discrete choice model to test hypotheses of homophily and status asymmetry. The results consistently support homophily hypotheses. It is found that different from friendship initiation which presents the pattern of both homophily and status asymmetry, friendship reciprocity is majorly driven by homophily. Furthermore, it is suggested that influence domain, popularity, grade and SES might be the major dimensions upon which homophily mechanism functions. |
