Which statement best describes perfect mediation?

Which statement best describes perfect mediation?

• A. The relationship between a predictor and an outcome is completely explained by a third variable.
• B. The mediator has no relation to either predictor or outcome.
• C. The predictor has a direct effect on the outcome even after including the mediator.
• D. The mediator is the outcome variable.

Answer: (A)

Mediation analysis asks whether a third variable explains how a predictor influences an outcome. Perfect mediation occurs when that third variable fully accounts for the relationship: once the mediator is included, the direct effect of the predictor on the outcome goes to zero, so the predictor affects the outcome only through the mediator. The statement “the relationship between a predictor and an outcome is completely explained by a third variable” captures this idea exactly. In real data you often see partial mediation, where some direct effect remains, but perfect mediation means there’s no remaining direct path after including the mediator.

Mediation analysis asks whether a third variable explains how a predictor influences an outcome. Perfect mediation occurs when that third variable fully accounts for the relationship: once the mediator is included, the direct effect of the predictor on the outcome goes to zero, so the predictor affects the outcome only through the mediator. The statement “the relationship between a predictor and an outcome is completely explained by a third variable” captures this idea exactly. In real data you often see partial mediation, where some direct effect remains, but perfect mediation means there’s no remaining direct path after including the mediator.