Participants were young adults in the sibling sample of the National Longitudinal Study of Adolescent Health. Detailed explanation of the study design and sampling strategy utilized for both the full sample and this genetically informative sub-sample are available elsewhere [Harris, Halpern, Smolen, & Haberstick, 2006; National Longitudinal Study of Adolescent Health, http://cpc.unc.edu/addhealth]. Initially, participants responded to an in-school survey in grades 7–12. Those who reported that they had a twin or a sibling (ages 12–20 years) with the same biological mother and father were identified and subsequently randomly selected for inclusion in an in-home interview sample. Within the twin and full-sibling sample, a total of 3,982 individuals participated in this initial in-home interview, with 3,297 participating 6 years later at wave III. Mean ages and ranges at these interviews were 16.2 (11 – 21), and 22.5 (18 – 27), respectively. The mean age difference between full-sibling pairs was 2.2 years (range 0.7 – 6.8). Self-reported maltreatment was assessed during wave III only. Of the individuals from 271 MZ twin pairs (128 male-male and 143 female-female), 397 DZ twin pairs (119
