Collider in RCT Subgroup Analysis

arthur_albuquerque:

I came across this interesting article: A proposal for capturing interaction and effect modification using DAGs

This was an opinion paper in IJE. I have decided to write a counter-opinion given so many (in my view ambiguous) attempts at inserting effect modification into DAGs. I will post the pre-print link here when done. Of note, a drug may work through a receptor to mediate a target effect e.g. GIP analogue through the GIPR, but the drug does not “cause“ the receptor as it exists whether or not the drug is present. Even though the drug doesn’t cause the receptor, the receptor is unambiguously the mechanism of action, and thus a mediator of its effect.