| Volume 2, Issue 2, 210-251, 2011 |
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|An SEM Perspective on Evaluating Mediation: What Every Clinical Researcher Needs to Know|
|University of Waterloo|
|Volume 2, Issue 2, 2011, Pages 210-251|
|After a brief consideration of the definition and importance of mediation, statistical tests for mediation are reviewed, including the joint significance of the two effects involved in the mediation, the Sobel test and its variants, resampling with the bootstrap, Bayesian estimation using MCMC simulation, and the effect ratio. A structural-equation-modeling (SEM) perspective on mediation then introduces the alternative scenarios that could yield a false-positive mediation finding. Design-based, partial solutions are advanced for problems of measurement, uncontrolled common causes, and temporal ordering that can confound mediation analysis. Next, the issue of heterogeneity of effects and statistical interactions in mediation analyses are addressed, including a discussion of moderated mediation and mediated moderation. Finally, the relation of mediation analysis to experimentation is discussed, with attention to the possibility of creatively integrating SEM-based mediation analysis and experimental design. |
|Table of Contents|
Statistical Tests of Mediation
Joint significance of the two paths involving the mediator.
Sobel test and its variants.
Resampling with the bootstrap.
Bayesian estimation using MCMC simulation techniques.
"Partial" versus "full" mediation and the effect ratio.
Recommendations and power.
How Hard is It to Pass a Statistical Test of Mediation?
The Need for Explicit Models
An SEM-Based Perspective on Mediation
Alternative Models Having to do with Measurement Issues
Alternative Models Having to do with Uncontrolled (Omitted) Common Causes
Alternative Models Having to do with Temporal Ordering
Implications of Alternative Models
Measuring and controlling for third variables.
Measuring and controlling for earlier levels of the same variables as in the model.
Heterogeneity and Interactions in the Evaluation of Mediation
Heterogeneity of Partial Slopes
Moderated Mediation and Mediated Moderation
The Relation between Mediation Analysis and Experimental Design
Integrating Mediation Analysis and Experimental Design
Appendix A: Demonstration of SEM-Based Methods for Evaluating Mediation
Joint significance of the two effects involved in the mediation.
Sobel test and its variants.
Bayesian estimation using the MCMC technique.
The effect ratio.
Appendix B: Demonstration of Two-Mediator, Two-Sample SEM and Contrasts Using Bayesian Custom-Estimands in Amos
|Erik Woody, Department of Psychology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. |
|Mediation; mediational analysis; bootstrap; Bayesian estimation; effect ratio; structural equation modeling; moderated mediation; mediated moderation; experimental design |
|Received 5 Aug 2010; Revised 26 Oct 2010; Accepted 26 Oct 2010; In Press 5 May 2011 |