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Why repeatedly extending a test inflates false positives

Source: interviewintermediate

WHAT IT TESTS: understanding the peeking problem and inflated false positives. OUTLINE: repeatedly checking and extending until significance is p-hacking via optional stopping, which inflates the false-positive rate; fix with fixed sample sizes or sequential…

WHAT IT TESTS: whether you recognize optional stopping as a statistical hazard. ANSWER OUTLINE: name it the peeking problem, a form of p-hacking. Fixed-horizon significance tests assume a sample size chosen in advance; repeatedly checking and extending until you hit significance multiplies the chances of a spurious result, inflating the false-positive rate well above the nominal level.

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Why repeatedly extending a test inflates false positives · Tezvyn