For the transition from no alcohol use to first full drink, participants entered the analysis at birth and “failed” at the age of their first drink, or were censored otherwise. For models of the timing of advanced transitions, individuals were included from the time of their first drink to the occurrences of the transition. To adjust for variability in risk period from age at first drink to other transitions, variables representing age at first drink (12 and younger, 13, 14, 15, 17, 18 and 19 and older; 16 was the median age and was used as the referent category) were included as covariates. Age categories were combined when their associations were not statistically different. (see Supplemental Tables 3-6). Risk factors and covariates were entered into the models simultaneously, and the same variables were included in all models. Violations of the proportional hazards assumption, that the hazard associated with a risk factor remains proportional over time, were investigated using Schoenfeld residuals as assessed by the Grambsch & Therneau test (Grambsch & Therneau, 1994). Identified violations were resolved by modeling age interactions
