Design a backtest that doesn't lie to you
Experiment designHardProblem. A teammate evaluated the new model with 5-fold cross-validation on two years of sales data and reports a 41% accuracy improvement. Leadership is excited. What do you say?
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.