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 University of Colorado’s Institutional Review Board, and parental and participant informed consent (as appropriate) was obtained at each wave of assessment (child assent was also obtained at age 12). Participants were paid $30 for the Wave 1 Center study, $50 for the Wave 2 Center study, and $50 for the executive function study.
