Effect size estimates: current use, calculations, and interpretation

The Publication Manual of the American Psychological Association (American Psychological Association, 2001, American Psychological Association, 2010) calls for the reporting of effect sizes and their confidence intervals. Estimates of effect size are useful for determining the practical or theoretic...

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Bibliographic Details
Published in:Journal of experimental psychology. General Vol. 141; no. 1; p. 2
Main Authors: Fritz, Catherine O, Morris, Peter E, Richler, Jennifer J
Format: Journal Article
Language:English
Published: United States 01.02.2012
Subjects:
Data Interpretation, Statistical
Humans
Research Design
Sample Size
Statistics as Topic
ISSN:1939-2222, 1939-2222
Online Access:Get more information
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Summary:The Publication Manual of the American Psychological Association (American Psychological Association, 2001, American Psychological Association, 2010) calls for the reporting of effect sizes and their confidence intervals. Estimates of effect size are useful for determining the practical or theoretical importance of an effect, the relative contributions of factors, and the power of an analysis. We surveyed articles published in 2009 and 2010 in the Journal of Experimental Psychology: General, noting the statistical analyses reported and the associated reporting of effect size estimates. Effect sizes were reported for fewer than half of the analyses; no article reported a confidence interval for an effect size. The most often reported analysis was analysis of variance, and almost half of these reports were not accompanied by effect sizes. Partial η2 was the most commonly reported effect size estimate for analysis of variance. For t tests, 2/3 of the articles did not report an associated effect size estimate; Cohen's d was the most often reported. We provide a straightforward guide to understanding, selecting, calculating, and interpreting effect sizes for many types of data and to methods for calculating effect size confidence intervals and power analysis.
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ISSN:1939-2222
1939-2222
DOI:10.1037/a0024338