Statistical properties of four effect-size measures for mediation models

Milica Miočević*, Holly P. O’Rourke, David P. MacKinnon, Hendricks C. Brown

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

131 Scopus citations


This project examined the performance of classical and Bayesian estimators of four effect size measures for the indirect effect in a single-mediator model and a two-mediator model. Compared to the proportion and ratio mediation effect sizes, standardized mediation effect-size measures were relatively unbiased and efficient in the single-mediator model and the two-mediator model. Percentile and bias-corrected bootstrap interval estimates of ab/sY, and ab(sX)/sY in the single-mediator model outperformed interval estimates of the proportion and ratio effect sizes in terms of power, Type I error rate, coverage, imbalance, and interval width. For the two-mediator model, standardized effect-size measures were superior to the proportion and ratio effect-size measures. Furthermore, it was found that Bayesian point and interval summaries of posterior distributions of standardized effect-size measures reduced excessive relative bias for certain parameter combinations. The standardized effect-size measures are the best effect-size measures for quantifying mediated effects.

Original languageEnglish (US)
Pages (from-to)285-301
Number of pages17
JournalBehavior Research Methods
Issue number1
StatePublished - Feb 1 2018


  • Bayesian methods
  • Bias
  • Effect sizes
  • Efficiency
  • Interval estimates
  • Mediation

ASJC Scopus subject areas

  • Experimental and Cognitive Psychology
  • General Psychology
  • Developmental and Educational Psychology
  • Arts and Humanities (miscellaneous)
  • Psychology (miscellaneous)


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