Data were drawn from the Missouri Adolescent Female Twin Study [16,20], a prospective study of female like-sex twin pairs born July 1975-June 1985 identified from Missouri-state birth records [N=370 African American (AA), 1999 European or (in rare cases) Other Ancestry (EA) pairs]. 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-four. In addition to baseline telephone interviews conducted with parents, all 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 detailed summary of response rates is provided elsewhere [16].
