Comparison of methods for constructing confidence intervals of standardized indirect effects
 Mike W. L. Cheung
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Abstract
Mediation models are often used as a means to explain the psychological mechanisms between an independent and a dependent variable in the behavioral and social sciences. A major limitation of the unstandardized indirect effect calculated from raw scores is that it cannot be interpreted as an effectsize measure. In contrast, the standardized indirect effect calculated from standardized scores can be a good candidate as a measure of effect size because it is scale invariant. In the present article, 11 methods for constructing the confidence intervals (CIs) of the standardized indirect effects were evaluated via a computer simulation. These included six Wald CIs, three bootstrap CIs, one likelihoodbased CI, and the PRODCLIN CI. The results consistently showed that the percentile bootstrap, the biascorrected bootstrap, and the likelihoodbased approaches had the best coverage probability. Mplus, LISREL, and Mx syntax were included to facilitate the use of these preferred methods in applied settings. Future issues on the use of the standardized indirect effects are discussed.
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 Title
 Comparison of methods for constructing confidence intervals of standardized indirect effects
 Journal

Behavior Research Methods
Volume 41, Issue 2 , pp 425438
 Cover Date
 20090501
 DOI
 10.3758/BRM.41.2.425
 Print ISSN
 1554351X
 Online ISSN
 15543528
 Publisher
 SpringerVerlag
 Additional Links
 Topics
 Industry Sectors
 Authors

 Mike W. L. Cheung ^{(1)}
 Author Affiliations

 1. Department of Psychology, Faculty of Arts and Social Sciences, National University of Singapore, Block AS4, Level 2, 9 Arts Link, 117570, Singapore