Psychology Commons^™

Assessing The Most Powerful Analysis Method For School-Based Intervention Studies, Jessica B. Janega, David M. Murray, Sherri P. Varnell, Jonathan L. Blitstein, Amanda Birnbaum, Leslie A. Lytle

Department of Public Health Scholarship and Creative Works

This article compares four mixed-model analyses valid for group-randomized trials (GRTs) involving a nested cohort design with a single pretest and a single posttest, the most common design used in GRTs. This study makes estimates of intraclass correlations (ICCs) available to investigators planning GRTs with alcohol, tobacco, and other drug measures as the outcomes of interest. It also provides formulae demonstrating the potential benefits to the standard error of the intervention effect of both adjustments for fixed and time-varying covariates, as well as correlations over time. These estimates will allow other researchers using these variables to plan their studies by …