We examined social mechanisms that account for similarity in the social context of school-sponsored extracurricular sports activities among friends. We distinguish two social mechanisms: “shared sports activities that lead to friendship,” whereby friendship formation and maintenance are conditioned by joint sports participation, and “friendship that leads to shared sports activities,” a form of social influence whereby adolescents join or maintain certain sports activities based on their friends' choices. Using a longitudinal sample of 1,776 10th graders at five high schools in Southern California, we employed a stochastic actor-oriented multivariate dynamic model to model the dynamic interplay between the two-mode affiliation network of adolescents' participation in sports activities and the one-mode friendship network. As a corresponding descriptive method, we propose a quantitative measure for the relative strength of the two-mentioned mechanisms as explanations of the association between the one-mode and the two-mode network. Further, we introduce two specifications that represent homophily effects in the two-mode network and apply them to test gender homophily in sports participation. The results provide strong evidence for both mechanisms, with friendship leading to shared sport activities as stronger than shared sports activities leading to friendships in explaining adolescents' friendships with co-participants.

Asymmetric ties make up a significant proportion of ties in friendship networks. But little is known about their origins. Prior research has suggested treating them either as “accidental” (e.g., resulting from constraints in name generators) or “aspirational” (i.e., the attempts of individuals to pursue relationships with higher status peers). In this paper, we show that self-perception can also explain the occurrence of asymmetric ties. We argue that under the general norm of reciprocity, actors with high self-perceived centrality will more likely send out ties to others than their counterparts. Supposing that outgoing ties are similarly reciprocated by peers, then actors with high self-perceived centrality will also entail more asymmetric ties. We test this idea along with the competing arguments using exponential random graph models (ERGMs) on network data collected from over 4,000 students in China. Consistent with previous findings, we find that asymmetric ties reflect status differences, but probably more strongly so for difference in individual status characteristics than difference in social positional status. More importantly, we find that students with high self-perceived centrality are about twice as likely to send asymmetric ties as their peers. Last, we examine the implications of our findings for future network research.

In empirical studies of friendship networks, participants are typically asked, in interviews or questionnaires, to identify some or all of their close friends, resulting in a directed network in which friendships can, and often do, run in only one direction between a pair of individuals. Here we analyze a large collection of such networks representing friendships among students at US high and junior-high schools and show that the pattern of unreciprocated friendships is far from random. In every network, without exception, we find that there exists a ranking of participants, from low to high, such that almost all unreciprocated friendships consist of a lower ranked individual claiming friendship with a higher ranked one. We present a maximum-likelihood method for deducing such rankings from observed network data and conjecture that the rankings produced reflect a measure of social status. We note in particular that reciprocated and unreciprocated friendships obey different statistics, suggesting different formation processes, and that rankings are correlated with other characteristics of the participants that are traditionally associated with status, such as age and overall popularity as measured by total number of friends.