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 grouprandomized 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.

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NSHAP's mental health measures were successfully integrated into the project's survey and showed acceptable external reliability as well as moderately stable individual characteristics across the 5 years between Waves 1 and 2. Depressive symptoms and unhappiness may form a mental health cluster in the elderly, distinct from anxiety symptoms, perceived stress, and felt loneliness. Gender differences in age-specific patterns of mental health were evident using the exact age of participants rather than the traditional decade groupings. Administration mode and time period (between 2005-2006 and 2010-2011) were determined to be potential confounds that need to be accommodated in longitudinal analyses of aging, whereas sample composition was not an issue for interpreting mental health measures.