title: A Statistical Method for Synthesizing Mediation Analyses Using the Product of Coefficient Approach Across Multiple Trials.
abstract: Mediation analysis often requires larger sample sizes than main effect analysis to achieve the same statistical power. Combining results across similar trials may be the only practical option for increasing statistical power for mediation analysis in some situations. In this paper, we propose a method to estimate: 1) marginal means for mediation patha, the relation of the independent variable to the mediator; 2) marginal means for pathb, the relation of the mediator to the outcome, across multiple trials; and 3) the between-trial level variance-covariance matrix based on a bivariate normal distribution. We present the statistical theory and an R computer program to combine regression coefficients from multiple trials to estimate a combined mediated effect and confidence interval under a random effects model. Values of coefficientsaandb, along with their standard errors from each trial are the input for the method. This marginal likelihood based approach with Monte Carlo confidence intervals provides more accurate inference than the standard meta-analytic approach. We discuss computational issues, apply the method to two real-data examples and make recommendations for the use of the method in different settings.
authors.affiliation: Department of Biostatistics, Vanderbilt University.
authors.forename: Shi
authors.initials: S
authors.lastname: Huang
authors.affiliation: Department of Psychology, Arizona State University.
authors.forename: David P
authors.initials: DP
authors.lastname: MacKinnon
authors.affiliation: Department of Public Health Sciences, University of Miami.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Perrino
authors.affiliation: Department of Preventive Medicine, Northwestern University.
authors.forename: Carlos
authors.initials: C
authors.lastname: Gallo
authors.affiliation: Department of Preventive Medicine, Northwestern University.
authors.forename: Gracelyn
authors.initials: G
authors.lastname: Cruden
authors.affiliation: Department of Preventive Medicine, Northwestern University.
authors.forename: C Hendricks
authors.initials: CH
authors.lastname: Brown
keywords: Data Synthesis; Mediation; Multiple trials; R; Restricted maximum likelihood