In a causal diagram, what composes the total causal effect?

• A. Direct and indirect causal path effects
• B. Indirect effects only
• C. Direct effects only
• D. No effect if mediators present

Answer: (A)

In a causal diagram, the total causal effect of an exposure on an outcome is the effect along all causal paths from the exposure to the outcome. This includes a direct path that goes straight from the exposure to the outcome, plus indirect paths that go through mediators. The sum of those direct and indirect path effects gives the total effect. Mediators don’t negate the effect; even with them present, you still have a total impact that combines both routes. If you only counted indirect effects, you’d miss the direct route; if you only counted direct effects, you’d miss what is transmitted through mediators.