Table 4 outlines the prevalence of having repeatedly used one or multiple substances in a person’s lifetime, the prevalence of being diagnosed with one or multiple SUDs (i.e., for different substances) in a person’s lifetime, and the expected prevalence of multiple repeated-use and SUDs at adolescence and young adulthood. The expected prevalence for multiple substances is computed on the assumption of independence among substances (details of the computation of the expected values to follow). The prevalence of lifetime multiple substance repeated-use and multiple SUDs increased between waves of assessment. Repeated-use of alcohol alone and alcohol SUDs alone were the most prevalent categories at each wave of assessment while “alcohol and marijuana” repeated-use was the most prevalent multiple substance repeated-use category at each wave. Of the multiple SUD categories, “tobacco and marijuana” was the most prevalent category at Wave 1 while “alcohol, tobacco, and marijuana” was the most prevalent category at Wave 2.
