Social Network Influences on Adolescent E-cigarette Use.

: Determine if individual adolescent vaping is associated with the vaping behavior of their school-based friendships; whether that association stems from peer influence or peer selection; and whether it varies by age. : Two wave longitudinal survey of 1,208 students in one Midwestern US school district. Students were asked if they ever vaped and to name their seven closest friends within the school district. A roster of all eligible students was pre-loaded into the survey to facilitate network data collection. Terms for network exposure, the proportion of vaping friends; and selection, the number of new friends who vape, were created. Logistic regression and Stochastic Actor Oriented Models were used to test both influence and selection effects. : A cross-sectional logistic regression model indicated that friend vaping was associated with individual vaping (AOR = 4.96,  < 0.01); and lagged logistic models indicated that increased friend vaping was associated with individual vaping initiation (AOR = 1.72,  < 0.05). Selecting new friends who vape was also associated with becoming a vaper (AOR = 1.25,  < 0.01). Both influence and selection were present for those less than 14 years old. : This is the first study to use social network analysis to show that adolescents who vape or initiate vaping are more likely to do so if their friends vape, and/or they make new friends who vape. Prevention and cessation programs should address the role of friend influence and selection on e-cigarette use; particularly at younger ages.