Your 90%-Precision Threshold Delivers 63.5% After a Prevalence Shift — With TPR and FPR Bit-Identical
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You tuned a decision threshold on validation to hit "precision at least 90%". You shipped it. The population's prevalence drifted from 10% to 2%. The model did not change. The scores did not change. TPR and FPR at that threshold are bit-identical — the same reduced fractions, 22663/29409 and 21043/…
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- 2026-09-08 08:29 · DEV Community — Machine Learning
Your 90%-Precision Threshold Delivers 63.5% After a Prevalence Shift — With TPR and FPR Bit-Identical