Our sample comes from the youngest cohort of the Finnish Twin Cohort Study (FinnTwin12), which was established to examine genetic and environmental factors influencing health-related behaviors (Kaprio, 2013), including the development of alcohol misuse. Participants were recruited from Finland’s Population Registry, permitting comprehensive and unbiased nationwide ascertainment of all twins born across five birth cohorts in Finland from 1983 to 1987. Baseline collection occurred when twins were aged approximately 12 years old, with a sample of some 5600 twins and their families (Kaprio, 2013) and an overall participation rate of 87%. Follow-up surveys occurred at ages 14, 17.5, and 22 years. Of the original epidemiological sample, 1035 families were chosen as part of an intensive subsample, from which 1852 twins (89% participation) completed the adolescent version of the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA; Bucholz et al., 1994) interview at age 14. Follow up of the intensive subsample when twins were, on average, age 22 (n=1347) included the adult SSAGA. DNA from blood or saliva samples was collected from 1295 twins. Data for the present study is drawn
