Design and analysis of the Community Youth Development Study longitudinal cohort sample.

Communities That Care (CTC) is a prevention system designed to reduce adolescent substance use and delinquency through the selection of effective preventive interventions tailored to a community's specific profile of risk and protection. A community-randomized trial of CTC, the Community Youth Development Study, is currently being conducted in 24 communities across the United States. This article describes the rationale, multilevel analyses, and baseline comparability for the study's longitudinal cohort design.