Which statement correctly differentiates confounding from mediation?

• A. Both biases distort the association in the same way.
• B. Confounding explains part of the causal pathway, while mediation distorts the exposure-outcome relationship.
• C. Confounding distorts the exposure-outcome relationship; mediation explains part of the causal pathway from exposure to outcome.
• D. Mediation is a type of bias that arises from misclassification.

Answer: (C)

Understanding the difference between confounding and mediation is key here. Confounding occurs when a third factor is related to both the exposure and the outcome and distorts the observed association, but it isn’t part of the causal path from exposure to outcome. Mediation describes a mechanism where the exposure changes an intermediate variable (the mediator), which then changes the outcome—the mediator is part of the causal pathway.

The best choice states exactly that: confounding distorts the exposure–outcome relationship, while mediation explains part of the causal pathway from exposure to outcome. It captures that confounding biases the observed association, whereas mediation reveals how the effect operates through an intermediate variable.

Why the other statements don’t fit: one option treats both as the same kind of bias, which isn’t accurate because mediation is about causal mechanism, not a bias. Another option wrongly assigns confounding to explain part of the causal pathway and says mediation distorts the relationship, which reverses the concepts. The last option incorrectly describes mediation as a bias arising from misclassification, which is not correct since mediation is about causal processes, not misclassification bias.