Evidence from both methods used to assess the existence of a generalized risk to use and abuse multiple substances supported the alternate forms and correlated liability models identified by Rhee and colleagues (2003, 2006). In many instances, the observed prevalence rates of multiple substance use and disorders were greater than the expected rates (derived under the assumption of independent liabilities). The comparison between the observed and expected rates revealed that (1) the factors contributing to these behaviors are not independent, and (2) the risk for use of multiple substances and the development of multiple SUDs increases with age. Similarly, the prediction models supported a model of generalized risk since SUDs on any substance in young adulthood could be predicted by involvement with any of the three substances in adolescence. Adolescent smoking not only increased an individual’s odds of developing tobacco/nicotine dependence, but also increased the odds of developing abuse or dependence on alcohol and marijuana in young adulthood. This finding was consistent with that of Bonomo and colleagues (2004) who also found an increased risk for alcohol dependence among tobacco
