Wasserstein distance measures how much probability mass must move, and at what cost, to transform one distribution into another. In monitoring, it acts as an alert for prediction drift and data drift rather than as a standalone model-quality measure. section 14.5.1
Retail drift monitoring
A retail system tests Wasserstein distance above 0.1 as a drift alert alongside Population Stability Index above 0.2. When comparing April 2021 with April 2022, it scales the control data by the expected 15% business growth before computing the distance. The same approach supports early warnings for next-day, next-week, and next-month predictions. section 14.5.1



