34–40 in the last wave of FinnTwin12 were recoded as 34–36=35 and 37–40=38). In AddHealth and COGA, we truncated the age range at 32, given the small number of observations outside this range. Based on the low prevalence of drinking initiation prior to adolescence and the ages/waves at which different cohorts had data available, we treated age 14 as the baseline for statistical models and excluded any data collected before this age. A timeline of the assessments for each cohort can be found in Figure 1 and Supplementary Table S1.
