Using cluster random assignment to measure program impacts - Statistical implications for the evaluation of education programs

This article explores the possibility of randomly assigning groups (or clus ters) of individuals to a program or a control group to estimate the impact s of programs designed to affect whole groups. This cluster assignment appr oach maintains the primary strength of random assignment-the provision of u nbiased impact estimates-but has less statistical power than random assignm ent of individuals, which usually is not possible for programs focused on w hole groups. To explore the statistical implications of cluster assignment, the authors (a) outline the issues involved, (b) present an analytic frame work for studying these issues, and (c) apply this framework to assess the potential for using the approach to evaluate education programs targeted on whole schools. The findings suggest that cluster assignment of schools hol ds some promise for estimating the impacts of education programs when it is possible to control for the average performance of past student cohorts or the past performance of individual students.