Mediator
A mediator is a variable M that is caused by some variable X and itself causes a variable Y.
Not to be confused with a moderator.
Contents
Description
Mediators are one possible failure of causal inference. A relationship has been identified between two variables, X and Y, but in actuality there is a mediator M between them. X causes M and M causes Y. This is called mediation.
The causal effects are:
direct effect of X on Y = β1
direct effect of X on M = β2
direct effect of M on Y = β3
indirect effect of X on Y = β2*β3
total effect of X on Y = β1 + (β2*β3)
See here for analysis of this system.