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Reevaluating R²med as an effect size measure for indirect effects
1Department of Business Administration, Jeonbuk National University.
Psychological Methods
|July 10, 2025
Summary
R²med accurately measures indirect effects, returning zero when none exist and distinguishing between mediation and suppression. This clarifies its utility and prevents misinterpretation of research findings.
Area of Science:
- Psychometrics
- Statistical Modeling
- Social Sciences Research Methods
Background:
- R²med is an effect size measure for indirect effects in mediation analysis.
- Previous research questioned its validity, citing potential for nonzero values without indirect effects and negative values.
Purpose of the Study:
- To clarify the properties and correct interpretation of the R²med effect size measure.
- To address criticisms regarding R²med's accuracy in detecting indirect effects and its handling of suppression.
Main Methods:
- Re-evaluation of R²med's mathematical properties in the context of mediation and suppression.
- Analysis of scenarios where indirect effects are absent or suppression is present.
Main Results:
- R²med correctly yields zero when no indirect effect is present.
- R²med distinguishes mediation (positive values) from suppression (negative values).
- Failure to recognize suppression can lead to misinterpretation of direct and indirect effects.
Conclusions:
- R²med is a valid and robust measure of indirect effect size.
- Its ability to differentiate mediation from suppression is a key strength, not a limitation.
- Correct interpretation of R²med enhances the accuracy of mediation and suppression effect analysis.
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