A routing change shipped country-wide — measure it without an A/B
Causal inferenceHardProblem. A payment-routing change went to a whole country at once (no randomized control). Give the causal method to measure its effect on approval and cost, and how you'd validate it.
Before you reveal: say your answer out loud, as if you were in the real interview — get your reasoning across clearly first. There is no single correct answer: reading what the interviewer is really after and defending your own thinking is what makes an answer strong.