Figure 5.

This figure illustrates conceptual differences between the third variables of moderator, mediator, covariate, and confound, adapting diagrams from Baron and Kenny (1986). As described in further detail in the text, a moderator is a third variable that changes the relationship between a predictor and outcome variable. Covariates do not alter but can clarify the relationship between predictor and outcome by adjusting for variance between a third variable and the outcome. On the other hand, mediators are third variables through which a predictor variable changes an outcome variable. Mediators may be distinguished from confounds, which are third variables that share the same statistical relationships but cannot reasonably be the cause by which the predictor affects change.