The sample consisted of African-American female twins who had participated in the Missouri Adolescent Female Twin Study (MOAFTS), a longitudinal study of alcohol-related problems and associated psychopathology in female adolescents and young adults. Female twin pairs born in Missouri between 1 July 1975 and 30 June 1985 to Missouri-resident parents were initially identified through birth records and recruited between 1995 and 1999 for the first wave of data collection. Recruitment was conducted using a cohort-sequential design, with cohorts of 13, 15, 17, and 19 year-old female twin pairs and their families ascertained in the first 2 years and new cohorts of 13 year-old twins and their families added in the subsequent 2 years. (For further details on ascertainment, see Heath et al., 2002). A special effort was made to ensure that the ethnic composition of the sample accurately reflected the population of Missouri, where approximately 14% of adolescents and young adults identify as African-American. In 2002–2005, all female twins from the target cohort (excluding those who had previously withdrawn from the study or whose parents had refused permission for the
