Participants (N = 3231, 52% female) were drawn from the Minnesota Twin Family Study (MTFS), a community-representative longitudinal study of Minnesota families. The study design has been extensively described elsewhere (Iacono & McGue, 2002), and is an accelerated-longitudinal design composed of two cohorts. The younger cohort (N = 2084, 50% female) was first assessed at age 11 during the years 1988–2005. The older cohort was first assessed at age 17 (N = 1147, 55% female) during the years 1989–1996. Members of the younger, 11-year-old cohort were invited to participate in follow-up assessments at age 14 and 17, and twins from both cohorts were invited to participate in follow-up assessments at age 20 and 24, for a total of five assessments spanning 13 years. Cohorts were combined for all analyses. Participants received modest honoraria for their assessments and written assent or consent was obtained from all participants, including the parents of minor children. From its inception, the study has been continuously approved by the University of Minnesota IRB.
