Data were drawn from the Missouri Adolescent Female Twin Study (Heath et al., 1999; 2002), a prospective study targeting the total cohort of female like-sex twin pairs born in Missouri to Missouri-resident parents, identified from birth records, for the period July 1, 1975-June 30, 1985 [N=370 African American (AA), 1999 European or other Ancestry (EA) pairs, the latter total including 26 of Asian/Pacific Islander or other ancestry]. A cohort-sequential sampling design was used, with initial cohorts of 13, 15, 17, and 19 year-old twins and their families recruited during the first two years of data-collection and continued recruitment of 13 year-olds in years three through four. In addition to baseline telephone diagnostic interviews conducted with parents, all available twin pairs were targeted for three waves of telephone interviews (Waves 1, 4 and 5, at median ages 15, 22 and 24, respectively). Subsamples of twins completed a brief one-year follow-up (Wave 2) and/or a three-year retest interview (Wave 3). For each wave, participants gave verbal consent (or assent if minors) following procedures approved by the institutional review board at Washington University. A summary of participation rates is provided elsewhere (Waldron et al., 2013).
