Medflex: An R package for flexible mediation analysis using natural effect models

Mediation analysis is routinely adopted by researchers from a wide range of applied disciplines as a statistical tool to disentangle the causal pathways by which an exposure or treatment affects an outcome. the counterfactual framework provides a language for clearly defining path-specific effects of interest and has fostered a principled extension of mediation analysis beyond the context of linear models. this paper describes medflex,an r package that implements some recent developments in mediation analysis embedded within the counterfactual framework. the medflex package offers a set of ready-made functions for fitting natural effect models,a novel class of causal models which directly parameterize the path-specific effects of interest,thereby adding flexibility to existing software packages for mediation analysis,in particular with respect to hypothesis testing and parsimony. in this paper,we give a comprehensive overview of the functionalities of the medflex package. © 2017,american statistical association. all rights reserved.