As part of preparing a revision for
this project, I have done a lot of reading and thinking about statistical mediation models. These models are often used when you wish to find the reason a manipulation exerts its impact on another variable -- the mechanism for the effect.
As I have described
elsewhere, let's say you have predictor variable $X$, outcome $Y$, and a variable $M$ that you think transmits the impact of $X$ on $Y$. You can think of this situation in terms of the following diagram: