Collider in RCT Subgroup Analysis

Pavlos_Msaouel:

See also here.

This was extremely helpful! I have a clarification question: In the example you give, if EGFR mutation was the only cause of oncogenic EGFR, would we still get a biased estimate in a subgroup of patients with oncogenic EGFR signaling? I would think not as in this instance this would be equivalent to an RCT in patients with EGFR mutation, would it not?

I’m also somewhat confused by the treatment indicator causing EGFR signaling. Temporally, I would assume EGFR signaling to already be present / absent before randomization (?) .