The consistency of peer and parent influences on tobacco, alcohol, and marijuana use among young adolescents.

The purpose of this study was to determine the degree to which the use of tobacco, alcohol, and marijuana by young adolescents can be described using a common theoretical model. Structural models were created in which psychosocial variables hierarchically predicted the use of each substance. The fit of a model in which paths from predictor variables were constrained to be equal was not inferior in any meaningful way to that of a model in which all path coefficients were freely estimated, thus suggesting that use of tobacco, alcohol, and marijuana by young adolescents may be considered to be a unitary phenomenon. A simplified model, in which these substances were combined into a single latent variable, showed a good fit. The results of these analyses suggest that it may be beneficial to consider adolescent substance use to be a unitary phenomenon.