not have any other siblings (64.6%) in the study, 55 (31.4%) had one, and 7 (4.0%) had two siblings in the study. The great majority was of European American descent (232; 95%) with 6 (2.5%) African American or biracial and 6 (2.5%) White Hispanic ancestry. Behavioral and alcohol or drug measures, appropriate for age, were extensively assessed on all family members at 3-year intervals. Written informed consent was obtained from the parents of all participants after the nature of the study had been explained to them; assent was also obtained from the offspring. The protocol was approved by the Institutional Review Board at the University of Michigan.
