38.2 Rule of Thumb for Causal Inference

To validly estimate the causal effect $X \to Y$:

• Close all backdoor paths between $X$ and $Y$ (paths that start with an arrow into $X$). This removes confounding.
• Do not block any part of the direct or indirect causal path from $X$ to $Y$ (especially via mediators).

This is known as the backdoor criterion—a formal condition from Pearl’s Causal Inference framework.