We report on a subset of twins in the LTS sample who have participated in two waves of study in the Colorado Center for Antisocial Drug Dependence, a longitudinal, multicomponent study ongoing at the Institute for Behavioral Genetics and the Addiction Research and Treatment Services at the University of Colorado. Current analyses are based on data from 584 adolescents from 293 same-sex twin pairs: 159 monozygotic (MZ) pairs (177 male and 139 female; 2 co-twins did not participate) and 134 dizygotic (DZ) pairs (138 males and 130 female). Twins were eligible for participation in Wave 1 of the Center studies after completing the sixth grade; the mean age at time of assessment was 12.4 years (SD = 0.36, range 11.3–14.0 years). Wave 2 assessments were completed at the 5-year follow-up, when the twins were approximately 17 years old (M = 17.4, SD = 0.62, range 16.5–20 years). At the Wave 2 testing session, twins were also assessed with a battery of executive function tasks under a separate protocol. All research protocols and consent forms were reviewed and approved by the
