References for Variance Almanac

Hedges, Larry V. & E. C. Hedberg. (2007). Intraclass correlation values for planning group-randomized trials in education. Educational Evaluation and Policy Analysis, 29(1), 60-87.

Experiments that assign intact groups to treatment conditions are increasingly common in social research. In educational research, the groups assigned are often schools. The design of group-randomized experiments requires knowledge of the intraclass correlation structure to compute statistical power and sample sizes required to achieve adequate power. This article 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 the statistical power of group-randomized experiments is illustrated.

Hedges, Larry V. & E. C. Hedberg. (2007). Intraclass correlations for planning group randomized experiments in rural education. Journal of Research in Rural Education, 22(10).

Experiments that assign intact groups (usually schools) to treatment conditions are increasingly common in educational research. The design of group randomized experiments requires knowledge of the intraclass correlation structure to compute statistical power and to determine the sample sizes required to achieve adequate power. The intraclass correlation structure of academic achievement is shown to be somewhat different in rural schools than in all schools in the nation. This article provides a compilation of intraclass correlation values of academic achievement and related covariate effects that could be used for planning group randomized experiments in rural schools. The use of these values to compute statistical power of group randomized experiments involving rural schools is illustrated.