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Understanding Power Anomalies in Mediation Analysis

Published online by Cambridge University Press:  01 January 2025

Kai WangOpen the ORCID record for Kai Wang[Opens in a new window]
Kai Wang*
Affiliation:
Department of Biostatistics, College of Public Health, The University of Iowa
*
Correspondence should be made to Kai Wang, Department of Biostatistics, College of Public Health, The University of Iowa, Iowa City, IA52242, USA. Email: kai-wang@uiowa.edu
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Abstract

Previous studies have found some puzzling power anomalies related to testing the indirect effect of a mediator. The power for the indirect effect stagnates and even declines as the size of the indirect effect increases. Furthermore, the power for the indirect effect can be much higher than the power for the total effect in a model where there is no direct effect and therefore the indirect effect is of the same magnitude as the total effect. In the presence of direct effect, the power for the indirect effect is often much higher than the power for the direct effect even when these two effects are of the same magnitude. In this study, the limiting distributions of related statistics and their non-centralities are derived. Computer simulations are conducted to demonstrate their validity. These theoretical results are used to explain the observed anomalies.

Keywords

mediationindirect effecttotal effectdirect effectpowerconsistency

Information

Type
Original Paper
Information
Psychometrika , Volume 83 , Issue 2 , June 2018, pp. 387 - 406
Copyright
Copyright © 2017 The Psychometric Society

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