title: Increasing Statistical Power in Mediation Models Without Increasing Sample Size.
abstract: Inadequate statistical power to detect treatment effects in health research is a problem that is compounded when testing for mediation. In general, the preferred strategy for increasing power is to increase the sample size, but there are many situations where additional participants cannot be recruited, necessitating the use of other methods to increase statistical power. Many of these other strategies, commonly applied to analysis of variance and multiple regression models, can be applied to mediation models with similar results. Additional predictors or blocking variables will increase or decrease statistical power, however, depending on whether these variables are related to the mediator, the outcome, or both. The effect of these two methods on the power for tests of mediation is illustrated through the use of simulations. Implications for health researchers using these methods are discussed.
authors.affiliation: Department of Educational Psychology, University of Nebraska, Lincoln, NE, USA matt.fritz@unl.edu.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Fritz
authors.affiliation: Department of Behavioral Science, M. D. Anderson Cancer Center, University of Texas, Houston, TX, USA.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Cox
authors.affiliation: Department of Psychology, Arizona State University, Tempe, AZ, USA.
authors.forename: David P
authors.initials: DP
authors.lastname: MacKinnon
mesh_terms: D006302:Health Services Research; D006801:Humans; D015233:Models, Statistical; D012107:Research Design; D018401:Sample Size
keywords: mediation; sample size; statistical power