Post-Deployment Monitoring of Prediction-Error Deterioration in Machine Learning Models Using a Two-Channel Exponentially Weighted Moving Average Chart
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Abstract
This study develops a forward-cross-fitted two-channel EWMA (FCF-DS-EWMA) chart for post-deployment monitoring of predictionerror deterioration in continuous-response machine-learning models. Temporally held-out Phase-I residuals are transformed into robust signed and magnitude channels, and an equal-share rule uses channel-specific finite-horizon limits whose common marginal exceedance level is selected jointly. In a unified Monte Carlo study with 𝑅 = 1000, the native false-alarm probability (PFA) is 0.176–0.196 for the in-sample-residual chart and 0.094–0.097 for FCF-DS across the three in-control environments. Six deterioration mechanisms are compared on a common ΔMSE scale. The signed and magnitude channels specialize to different changes, while equal-share calibration restores directional sensitivity relative to a common-limit maximum (abrupt-shift detection probability 𝑃𝐷 = 0.724 versus 0.582). One-factor analyses of native PFA identify serial dependence, inadequate block length, and monitoring horizon as the clearest sources of false-alarm inflation. An oracle diagnostic shows that the temporary-model/final-model reference mismatch mainly shifts the operating point by a small amount. The ethanol study illustrates channel attribution and reference-location sensitivity, and paired perturbations of actual post-Phase-I Metro traffic residual windows provide quantitative evidence in a second regression domain.
Keywords
prediction-error monitoring, cross-fitting, EWMA, control chart, residual monitoring, statistical process monitoring
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