Demystifying omega squared: Practical guidance for effect size in common analysis of variance designs

Omega squared (ω^2) is a measure of effect size for analysis of variance (ANOVA) designs. It is less biased than eta squared, but reported less often. This is in part due to lack of clear guidance on how to calculate it. In this paper, we discuss the logic behind effect size measures, the problem wi...

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Vydané v:Psychological methods Ročník 30; číslo 4; s. 866
Hlavní autori: Kroes, Antoinette D A, Finley, Jason R
Médium: Journal Article
Jazyk:English
Vydavateľské údaje: United States 01.08.2025
Predmet:
Analysis of Variance
Data Interpretation, Statistical
Humans
Psychology - methods
Research Design
ISSN:1939-1463, 1939-1463
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Shrnutí:Omega squared (ω^2) is a measure of effect size for analysis of variance (ANOVA) designs. It is less biased than eta squared, but reported less often. This is in part due to lack of clear guidance on how to calculate it. In this paper, we discuss the logic behind effect size measures, the problem with eta squared, the history of omega squared, and why it has been underused. We then provide a user-friendly guide to omega squared and partial omega squared for ANOVA designs with fixed factors, including one-way, two-way, and three-way designs, using within-subjects factors and/or between-subjects factors. We show how to calculate omega squared using output from SPSS. We provide information on the calculation of confidence intervals. We examine the problems of nonadditivity, and intrinsic versus extrinsic factors. We argue that statistical package developers could play an important role in making the calculation of omega squared easier. Finally, we recommend that researchers report the formulas used in calculating effect sizes, include confidence intervals if possible, and include ANOVA tables in the online supplemental materials of their work. (PsycInfo Database Record (c) 2025 APA, all rights reserved).
Bibliografia:ObjectType-Article-1
SourceType-Scholarly Journals-1
ObjectType-Feature-2
content type line 23
ISSN:1939-1463
1939-1463
DOI:10.1037/met0000581