Causal mediation analysis: what is it and how can it be used to inform practice and policy?

Background: Causal mediation, a quantitative analysis method, has the potential to be a valuable addition to any primary care provider, researcher, or student's toolbox.

Objective: This manuscript describes the theory behind causal mediation, provides a running example to help understand the application of this method in research, and explains how the results may be applied practically to help design appropriate interventions.

Methods and application: Causal mediation allows an exploration of the mechanism of action of a primary care intervention on an outcome that may pass through a third variable that is on the causal pathway, a mediator. Causal mediation analysis allows the decomposition of the total effect of an intervention on an outcome into both direct and indirect effects. Careful interpretation of generated results can guide decision-makers when devising or refining interventions or policies that affect patient health outcomes in primary care.

Conclusion: Causal mediation has been used in many disciplines and is well-positioned to answer varied research questions. However, the full extent of its potential has yet to be realized.