RMediation: an R package for mediation analysis confidence intervals

Abstract

This article describes the RMediation package,which offers various methods for building confidence intervals (CIs) for mediated effects. The mediated effect is the product of two regression coefficients. The distribution-of-the-product method has the best statistical performance of existing methods for building CIs for the mediated effect. RMediation produces CIs using methods based on the distribution of product, Monte Carlo simulations, and an asymptotic normal distribution. Furthermore, RMediation generates percentiles, quantiles, and the plot of the distribution and CI for the mediated effect. An existing program, called PRODCLIN, published in Behavior Research Methods, has been widely cited and used by researchers to build accurate CIs. PRODCLIN has several limitations: The program is somewhat cumbersome to access and yields no result for several cases. RMediation described herein is based on the widely available R software, includes several capabilities not available in PRODCLIN, and provides accurate results that PRODCLIN could not.

Fig. 1

Kernel density plot of the distribution of the product of two normal variables (i.e., mediated effect) and the 90% CI with error bars for the mediated effect, with â = 0.295, b̂ = 1.673, SE(â) = 0.163, and SE(b̂) = 0.695. LL lower limit, UL upper limit