Mediating Variables

A mediator variable is specified as a causal mechanism between two other variables. In many fields, researchers have observed simple causal relations between a predictor variable (X) and a criterion variable (Y). Although demonstrating that such a relation exists can certainly advance our understanding of phenomena, there are often intervening variables that, for any number of reasons, remain unstudied. In such situations, researchers attempt to identify these intervening variables that serve to mediate the relation between X and Y. Such a variable is referred to as a mediator (M).

In specifying a mediation model, the researcher must be able to advance a rational/theoretical argument as to why the mediator should be included. Fundamentally, models involving mediation are causally specified. That is, X causes M, which, in ...