Intraclass Correlation Values for Planning Group Randomized Trials in Education (WP-06-12)
Larry V. Hedges and Eric C. Hedberg
Experiments that assign intact groups to treatment conditions are increasingly common in social research. In educational research, the assigned groups are often schools. The design of group randomized experiments requires knowledge of the intraclass correlation structure to compute the statistical power and sample sizes needed to achieve adequate power. This working paper provides a compilation of intraclass correlation values of academic achievement and related covariate effects that could be used for planning group randomized experiments in education. It also provides variance component information that is useful in planning experiments involving covariates. The use of these values to compute statistical power of group randomized experiments is illustrated as well.