Analysis strategies for a community trial to reduce adolescent ATOD use: a comparison of random coefficient and ANOVA/ANCOVA models.

The Community Youth Development Study (CYDS) will evaluate the Communities That Care (CTC) operating system for its effects on alcohol, tobacco, drug use, and other outcomes among adolescents resident in the 24 participating communities. The CYDS employs a combination of both cross-sectional and cohort designs. We use data from an earlier study that included the CYDS communities to estimate power for CYDS intervention effects given several analytic models that might be applied to the multiple baseline and follow-up surveys that define the CYDS cross-sectional design. We compare pre-post mixed-model ANCOVA models against random coefficients models, both in one- and two-stage versions. The two-stage pre-post mixed-model ANCOVA offers the best power for the primary outcomes and will provide adequate power for detection of modest but important intervention effects.