as the study is ongoing, non-participation in subsequent waves is not necessarily indicative of attrition. However, analyses of those who were eligible to have participated in the 6 year follow-up found no significant differences related to substance use behaviors or psychiatric characteristics. We also adjusted for number of follow-ups in all analyses. Third, recall bias may have influenced reports of all variables, particularly age of onset. We attempted to ameliorate this concern by using multiple reports of age of onset and selecting the one that was closest in age to the age of the respondent at the time of the interview. This may have resulted in higher ages being ascribed to onset. On average, the difference between first, earliest and the age of onset selected by us, for any variable, was 1 year. Fourth, as we required independent variables (and covariates) to be time-varying, we were only able to focus on early substance use as “predictors” of SI and SA, as the onset age for SI and SA was fairly low and typically preceded the onset of substance use and dependence. That is, in many instances, the typical age of onset of substance use and dependence occurred after the onset
