title: Tests of Mediation: Paradoxical Decline in Statistical Power as a Function of Mediator Collinearity.
abstract: Increasing the correlation between the independent variable and the mediator (acoefficient) increases the effect size (ab) for mediation analysis; however, increasingaby definition increases collinearity in mediation models. As a result, the standard error of product tests increase. The variance inflation due to increases inaat 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 ofabapproximates the variance expected from normal theory. Both variances increase dramatically whenaexceeds thebcoefficient, thus explaining the power decline with increases ina. Implications for statistical analysis and applied researchers are discussed.
authors: University of Alabama at Birmingham.
authors: T Mark
authors: TM
authors: Beasley
keywords: Bootstrap; Collinearity; Mediation Analysis; Power; Tolerance