title: Causal mediation analysis with a binary outcome and multiple continuous or ordinal mediators: Simulations and application to an alcohol intervention.
abstract: We investigate a method to estimate the combined effect of multiple continuous/ordinal mediators on a binary outcome: 1) fit a structural equation model with probit link for the outcome and identity/probit link for continuous/ordinal mediators, 2) predict potential outcome probabilities, and 3) compute natural direct and indirect effects. Step 2 involves rescaling the latent continuous variable underlying the outcome to address residual mediator variance/covariance. We evaluate the estimation of risk-difference- and risk-ratio-based effects (RDs, RRs) using the ML, WLSMV and Bayes estimators in Mplus. Across most variations in path-coefficient and mediator-residual-correlation signs and strengths, and confounding situations investigated, the method performs well with all estimators, but favors ML/WLSMV for RDs with continuous mediators, and Bayes for RRs with ordinal mediators. Bayes outperforms WLSMV/ML regardless of mediator type when estimating RRs with small potential outcome probabilities and in two other special cases. An adolescent alcohol prevention study is used for illustration.
authors.affiliation: Department of Mental Health, Johns Hopkins Bloomberg School of Public Health.
authors.forename: Trang Quynh
authors.initials: TQ
authors.lastname: Nguyen
authors.affiliation: Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health.
authors.forename: Yenny
authors.initials: Y
authors.lastname: Webb-Vargas
authors.affiliation: Department of Interdisciplinary Social Science, University of Utrecht.
authors.forename: Ina M
authors.initials: IM
authors.lastname: Koning
authors.affiliation: Department of Mental Health, Johns Hopkins Bloomberg School of Public Health; Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health; Department of Health Policy and Management, Johns Hopkins Bloomberg School of Public Health.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Stuart
keywords: binary outcome; causal mediation analysis; continuous mediators; multiple mediators; ordinal mediators; structural equation modeling