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Peeking in A/B tests and how to mitigate it

Source: interviewintermediate

WHAT IT TESTS: understanding inflated false positives from repeated looks. OUTLINE: peeking is checking significance repeatedly and stopping at the first significant result, which inflates false positives; mitigate with fixed sample sizes or sequential…

WHAT IT TESTS: whether you understand that repeatedly testing significance and stopping when it first crosses the threshold dramatically inflates the false-positive rate. ANSWER OUTLINE: define peeking, explain why each look is another chance to cross 0.05 by luck so the true error rate far exceeds the nominal one, and give mitigations: pre-compute a fixed sample size and decide only at the end, or use methods designed for continuous monitoring like sequential testing or always-valid confidence intervals.

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Peeking in A/B tests and how to mitigate it · Tezvyn