represent a fully articulated behavioral genetic design. These pairs of adolescents took the same questionnaires, share the same home environment, and share, in most cases, the same school and neighborhood environment. The embedded sibling pairs design in Add Health and the data available for sibling pairs are unprecedented for a U.S. study of this magnitude. In all follow-up interviews, high priority has been placed on locating and re-interviewing sibling pairs to maintain the integrity of this subsample for longitudinal research purposes.
