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Correction to Wen and Fan (2015)

    Psychological Methods
    |May 12, 2015
    PubMed
    Summary

    Kappa-squared (κ²) is not a reliable effect size measure for mediation analysis due to its lack of monotonicity and potential for paradoxical results. Researchers should consider alternative measures like PM for mediation effect size.

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    Area of Science:

    • Psychological Methods
    • Social and Behavioral Sciences

    Context:

    • Mediation analysis is crucial in psychology and related fields.
    • Assessing mediation effect sizes is an ongoing area of research.
    • Kappa-squared (κ²) was proposed as a mediation effect size measure.

    Purpose:

    • To critically evaluate kappa-squared (κ²) as a measure of mediation effect size.
    • To demonstrate the limitations and potential paradoxes associated with κ².
    • To suggest alternative approaches for mediation effect size measurement.

    Summary:

    • This article argues that κ² lacks the property of rank preservation, meaning its magnitude can decrease as the mediation effect increases.
    • The mathematical definition of κ² is flawed due to an improper calculation of the maximum indirect effect, which can be infinite.
    • κ² can yield paradoxical results in multiple mediation models, questioning its utility.

    Impact:

    • Highlights the inappropriateness of κ² as a universal mediation effect size measure.
    • Recommends considering the traditional PM measure for basic mediation models.
    • Underscores the need for careful selection of effect size measures in mediation analysis, especially for inconsistent models.

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