genes and environment on substance use and related milestones in youth and young adults, most of whom (86.7%) are at high familial risk for alcoholism. In 2005, adolescent and young adult offspring born from 1982 onwards were recruited from alcoholic and control COGA families described above. The prospective study was designed to be conducted on offspring of ages 12–22 years at their baseline assessment, with at least one parent who was interviewed in the first phases of the parent COGA study. Subsequent assessments occur every two years with data available on 3,277 participants (aged 12–26 years; there were some offspring who required repeat tracking and multiple invitations over several years to participate in the baseline interview and as a result 1.3% of offspring were older than age 22 at their first interview). Currently, 2759, 2238, 1733, 1093 and 409 individuals have participated in the 2, 4, 6, 8 and 10 year follow-ups respectively, reflecting data collected between January 2005 and June 2016. For the present study, we used all available data, across all interviews, such that as long as individuals had participated in the baseline, their data were included.
