Subjects in the study were 1733 individual members of twin pairs drawn from the Colorado Community Twin Study (CTS) and Longitudinal Twin Study (LTS) who also participated in the Center for Antisocial Drug Dependence (CADD) study at the University of Colorado (Rhea et al., 2006). Participants in this study are part of a community-based twin sample of individuals that had completed two waves of assessment. The CTS sample was identified for recruitment through the Colorado Department of Health (CDH), Division of Vital Statistics, supplemented later by Colorado school districts. All members of the LTS were recruited at birth through the CDH and most have participated in the study repeatedly from infancy to the present. A total of 1142 CTS and 591 LTS respondents participated at both waves. Details of the recruitment procedures are provided by Rhea et al. (2006).
