Title: Power Calculations for Binary Moderator in Cluster Randomized Trials Authors and Affiliations: Jessaca Spybrook Western Michigan University

Background / Context: Cluster randomized trials (CRTs), or studies in which intact groups of individuals are randomly assigned to a condition, are becoming more common in the evaluation of educational programs, policies, and practices. For example, a search on the website for the Institute of Education Sciences (IES) suggests that the National Center for Educational Research (NCER) funded around 7 randomized trials in 2004. The same search for 2011 yielded around 36 funded randomized trials, or approximately 5 times as many trials. The website for the National Center for Education Evaluation and Regional Assistance (NCEE) reveals they have launched over 30 evaluation studies in the past decade, the majority of them utilizing a randomized trial. Clearly there are a large number of randomized trials of educational programs, policies, and practices either complete or currently in the field.