Intraclass correlation values for planning group-randomized trials in education

Larry V. Hedges, E. C. Hedberg

Research output: Contribution to journalArticlepeer-review

594 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)60-87
Number of pages28
JournalEducational Evaluation and Policy Analysis
Issue number1
StatePublished - Mar 2007
Externally publishedYes


  • Cluster randomized trials
  • Experiments
  • Intraclass correlation
  • Statistical power

ASJC Scopus subject areas

  • Education


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