The sample was composed of 3,761 female twins who completed the fourth wave of data collection for the Missouri Adolescent Female Twin Study (MOAFTS). Female twins born in Missouri to Missouri-resident parents between 1975 and 1985 were identified through birth records and recruited between 1995 and 1999 for the MOAFTS Wave 1 assessment. Cohorts of 13, 15, 17, and 19 year-old female twin pairs and their families were ascertained in the first two years. New cohorts of 13 year-old twins and their families were added in the subsequent two years. Parent interviews were completed by 78% of targeted families. (See Heath et al. (34) for details on ascertainment). Wave 3 retest interviews were administered to a subset of Wave 1 participants two years after Wave 1 assessments. (Data were not drawn from Wave 2, which covered only the previous 24 months.) Wave 4 interviews were conducted from 2002 to 2005. Wave 5 assessments were conducted from 2005 to 2008. Of the 4,638 twins identified from birth records, 80% completed the Wave 4 interview (n=3,787), the primary source of data for
