NotesFAQContact Us
Search Tips
Peer reviewed Peer reviewed
Direct linkDirect link
ERIC Number: EJ1028165
Record Type: Journal
Publication Date: 2014
Pages: 24
Abstractor: As Provided
Reference Count: 50
ISSN: ISSN-0022-0973
Tests of Mediation: Paradoxical Decline in Statistical Power as a Function of Mediator Collinearity
Beasley, T. Mark
Journal of Experimental Education, v82 n3 p283-306 2014
Increasing the correlation between the independent variable and the mediator ("a" coefficient) increases the effect size ("ab") for mediation analysis; however, increasing a by definition increases collinearity in mediation models. As a result, the standard error of product tests increase. The variance inflation caused by increases in "a" at some point outweighs the increase of the effect size ("ab") and results in a loss of statistical power. This phenomenon also occurs with nonparametric bootstrapping approaches because the variance of the bootstrap distribution of "ab" approximates the variance expected from normal theory. Both variances increase dramatically when a exceeds the "b" coefficient, thus explaining the power decline with increases in "a". Implications for statistical analysis and applied researchers are discussed.
Routledge. Available from: Taylor & Francis, Ltd. 325 Chestnut Street Suite 800, Philadelphia, PA 19106. Tel: 800-354-1420; Fax: 215-625-2940; Web site:
Publication Type: Journal Articles; Reports - Research
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A