arXiv Machine Learning By Jia Huang, Yankai Wan, Yangjun Ou

Prevalence Determines Precision:Silent Contamination in Detector-Defined Datasets

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The paper shows that when machine‑learning datasets are built by applying a detector to a candidate pool, the precision of the resulting labels is largely determined by the prevalence of true positives in that pool, not just the detector’s accuracy. In a study using one detector across three different pools, phantom (false) rates varied from 81.7% to 0%, and the Bayes‑based precision estimate matched all three pools within 3.3%, whereas naive transfer of precision from high‑rate pools over‑estimated precision by 422%. The authors further demonstrate that contamination behaves as a second signal with the detector’s shape, affecting different estimators in opposite ways, and that common normalizations can produce misleading results.

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