📊 The standard advice for model monitoring doesn't work in production.

Retraining monthly misses slow degradation. Arbitrary PSI thresholds cause alert fatigue. You get an alert. Is it a data pipeline bug, covariate drift, or concept drift? No one knows.

The latest Data Letter breaks down five drift detection methods (PSI, Wasserstein, KL, MMD, Page-Hinkley) by the specific question each one answers. It's a guide to choosing the right statistical tool.