Estimation of effect size from a series of independent experiments

Larry V. Hedges*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

709 Scopus citations


Extends statistical theory for procedures based on the Glass estimator of effect size for methods used in the quantitative synthesis of research. An unbiased estimator of effect size is given. A weighted estimator of effect size based on data from several experiments is defined and shown to be optimal (asymptotically efficient). An approximate (large-sample) test for homogeneity of effect size across experiments is also given. The results of an empirical sampling study show that the large-sample distributions of the weighted estimator and the homogeneity statistic are quite accurate when the experimental and control group sample sizes exceed 10 and the effect sizes are smaller than about 1.5. (12 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).

Original languageEnglish (US)
Pages (from-to)490-499
Number of pages10
JournalPsychological bulletin
Issue number2
StatePublished - Sep 1982


  • estimation of effect sizes for 2 or more independent studies

ASJC Scopus subject areas

  • General Psychology


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