Understanding how health interventions or exposures produce their effects using mediation analysis

The reasons that health exposures, such as medical interventions, change patient outcomes are often poorly understood. Health exposures change patient outcomes through biological, psychological, and social mediators. Generally, a mediator is a variable that lies on the causal path between an exposure and an outcome. The causal role of a mediator can be communicated through a directed acyclic graph,1 which visually represents the direction of causal effects from exposures to outcomes and distinguishes between other variables such as confounders and colliders2 (fig 1). In health research, identifying mediators has the potential to inform theory, optimise interventions, and facilitate the implementation of policies and interventions in clinical and public health practice.3 The value of identifying the mediators of health interventions has been noted by the UK National Institute for Health and Care Research and the US National Institutes of Health.45 The mediators of health exposures in randomised trials and observational studies…
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