Perception of peer substance use was measured using 4 items adapted from the FinnTwin12 study (Kaprio et al. 2002), included as part of the C-SSAGA. These questions asked participants about how many of their best friends smoke, use alcohol, use marijuana, and use other drugs. Responses were rated on a 4-point scale from 1 (none of them) to 4 (all of them). Cronbach’s alphas were .77 and .79 for T1 and T2, respectively. Items were averaged, and higher scores indicated higher levels of perceived peer substance use.
