Over time relationships between early adolescent and peer substance use

Peer and adolescent substance use are highly correlated, but this relationship is not fully understood. In particular, the relative contributions of selection and socialization to substance use progression have not been established. Students (n = 2453) in the seven middle schools in one school district were assessed at school at the beginning and end of the sixth, seventh, eighth grade and beginning of the 9th grade. Self-reported smoking and drinking and the number of substance using friends were assessed 5 times over 3 years. The relationship between peer and adolescent substance use were assessed in parallel processes as part of an autoregressive latent trajectory model. Substance use and the number of substance using friends increased in linear fashion from T1 to T5. Initial substance use predicted an increase in the number of substance using friends over time, indicating an effect of selection, and the initial number of substance using friends predicted substance use progression, providing evidence of socialization. The magnitudes of these relationships were similar. Bivariate, lagged autoregressive analyses of the successive relationships from one assessment to the next showed consistent, significant associations from peer use to adolescent substance use. The association from adolescent to peer use was significant only from 7th to 8th grade. The findings provide evidence of reciprocal influences, but socialization was a more consistent influence than selection.