Work

Tests of Mediation: Paradoxical Decline in Statistical Power as a Function of Mediator Collinearity

Year: 2013

Type: article

Abstract: 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.

Source: The Journal of Experimental Education

DOI: 10.1080/00220973.2013.813360

Author: T. Mark Beasley

Institutions: United States Department of Veterans Affairs, University of Alabama at Birmingham, Department of Veterans Affairs

Language: English

Topic: Advanced Causal Inference Techniques

Subfield: Statistics and Probability

Field: Mathematics

Domain: Physical Sciences

Open Access status: green

Funder: National Institute of Arthritis and Musculoskeletal and Skin Diseases

Award: NIAMS Multidisciplinary Clinical Research Center