Suppression and mediation effect in psychosocial intervention: Differences, similarities and examples

This paper compares the mediator and suppressor effect of a third variable. Both effects split the variance of the dependent variable (Y). Mediation is the reduction, after introducing the third variable (Z) in the model, of the proportion of variance explained on variable Y directly by the independent variable (X), and suppression is the increase of the of the proportion of variance explained on variable Y directly by the independent variable after introducing the third variable in the model. Then, the characteristics and differences of each effect are analyzed and the situations in which either effect occurs are examined. Each situation, consisting of three intercorrelated variables, is explained with examples from the psychosocial intervention context. Finally, recommendations for the use and interpretation of both effects are provided