Peer selection and influence for marijuana use in a complete network of first-year college students

Marijuana is the most frequently used illicit drug among college students, and there is a need to understand the social processes that contribute to young adults' marijuana use. Substance use behaviors tend to be more similar (homophilous) among individuals with social ties to one another. However, little is known about whether marijuana use homophily within young adult relationships is due to social selection (seeking out ties with similar marijuana use to one's own) or social influence (adopting similar marijuana use behaviors as one's ties), or both.

Students (N = 1,489; 54.6% female; M_age = 18.6 years) at one University completed online surveys in their first three semesters of college. Surveys assessed participant characteristics, marijuana use, and ties to up to 10 other students in the whole (sociocentric) network of first-year college students. Stochastic-actor oriented models (SAOMs) were used to analyze the co-evolution of marijuana use and social ties over time.

Participants were more likely to select peers with similar past 30-day marijuana use as themselves. Concurrently, students' past 30-day marijuana use became more similar to their peers' use over time.

Evidence for selection and influence effects were highly significant after controlling for network structure and other covariates indicating these processes may work in tandem to increase marijuana use homophily over the first year of college. This highlights the importance of relationships made early in the first-year of college, as these initial peer ties are likely to reinforce marijuana use behaviors that occur within these relationships.