The sample was comprised of 1,716 female twins who participated in the Missouri Adolescent Female Twin Study (MOAFTS) and reported an age at first drink in at least 2 of the 3 waves of data collection in which lifetime drinking histories were gathered. MOAFTS is a longitudinal study of alcohol-related problems and associated psychopathology in female adolescent and young adult twins born in Missouri between 1975 and 1985. Twins were identified through birth records and recruited for the first wave of data collection between 1995 and 1999. Cohorts of 13, 15, 17, and 19 year-old female twin pairs and their families were ascertained using a cohort-sequential design. (See Heath et al. (2002) for details). Lifetime alcohol use history was queried in Waves 1, 3, and 4. Wave 3 interviews were conducted with the first 8 6-month cohorts who completed Wave 1, approximately 2 years after completion of Wave 1 interviews, to assess retest reliability of the interview. All twins from the target cohort (excluding those who had withdrawn from the study or whose parents had refused permission to re-contact the
