1. Introduction
POF
Studies in the health and behavioural sciences often aim to understand whether and, if so, how an intervention causes an outcome. The randomised controlled trial is considered the most rigorous method for answering the "whether" question, but often the "how" part remains unclear. Causal mediation analysis plays an important role in understanding the mechanism by which an intervention produces changes in the outcome. Understanding how an intervention works can be key for further improvement and targeting of an intervention program.There is a fast-growing methodological literature on causal mediation analysis [Within the POF, the regression-based [Recently, Bayesian modelling has been introduced to the mediation analysis literature [