Influences on Boys' Marijuana Use in High School: A Two-Part Random Intercept Growth Model

This study examined differences in predictors of marijuana use versus quantity of marijuana use across the high school years, using annual assessments from the Oregon Youth Study (OYS) and a two-part model for semicontinuous data. The OYS is a community sample of at-risk boys followed from age 10 years. In order to capture dynamic prediction effects, change scores of predictors, as well as baseline scores, were included. Baseline predictors predominantly showed associations with the intercepts but not with the slopes of growth models. Change scores for parental monitoring, peer substance use, and antisocial behavior and deviant associations were associated with both parts of the model. Findings highlight the importance of looking at marijuana use compared to quantity of marijuana use.