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.