“predicted” onset of SI and SA, as has been frequently done in prior longitudinal studies. We elected to focus on early substance use for Model 1 because, as shown in Supplemental Figures, the median age of onset of SI and SA preceded the typical median age of onset of alcohol, nicotine and cannabis use. In contrast, in Models 2–3, substance involvement measures were the dependent variables, and we examined the reciprocal pathway from SI and SA to onset of substance use and dependence.
