Size a Feastables in-store test across stores
Power & sample sizeMediumProblem. Feastables wants to test a new in-store display at one retailer. Stores would be randomly split; sales are measured as units per store per week over six weeks. The team hopes to detect a 5% lift. Stores sell about 40 units a week on average, but vary a lot. How many stores do you need?
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.