What makes up the total causal effect in a causal diagram?

• A. No effect in causal diagrams
• B. Indirect effect only
• C. Direct + indirect causal path effects
• D. Direct effect only

Answer: (C)

The total causal effect is the overall change in the outcome when you intervene to set the exposure, accounting for every route by which the exposure influences the outcome. In a causal diagram, that means adding the direct effect (the path from the exposure straight to the outcome) to all indirect effects that operate through mediators via directed paths from the exposure to the outcome. So the total effect is the sum of the direct effect and all indirect effects along all causal paths.

This explains why focusing only on the direct path misses mediated influence, and focusing only on indirect paths misses any direct influence. And “no effect” would be incorrect because the diagram implies there can be causal pathways linking exposure to outcome.