Expansion ARR is heavy-tailed. Size a test on 4,000 accounts.
Power & sample sizeMediumProblem. Customer success wants to test a proactive adoption program on 4,000 mid-size accounts, half treated, over two quarters. The outcome they care about is expansion ARR per account. The average is $8,000, but a handful of accounts expand by hundreds of thousands. Can the test detect a 20% lift? If not, what would you change?
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.