What are effect sizes and why do we need them?

Larry V. Hedges*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


Effect sizes are quantitative indexes of the relations between variables found in research studies. They can provide a broadly understandable summary of research findings that can be used to compare different studies or summarize results across studies. Unlike statistical significance (p values), effect sizes represent strength of relationships without regard to sample size. Three families of effect sizes are widely used: the standardized mean difference family, the standardized regression coefficient family, and the odds ratio family.

Original languageEnglish (US)
Pages (from-to)167-171
Number of pages5
JournalChild Development Perspectives
Issue number3
StatePublished - Dec 2008


  • Effect size
  • Metaanalysis
  • P values
  • Statistical significance
  • Statistics

ASJC Scopus subject areas

  • Developmental and Educational Psychology
  • Life-span and Life-course Studies
  • Pediatrics, Perinatology, and Child Health


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