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Introduced on day 19

Data drift (covariate shift)

A change in the distribution of the model's inputs between training and production; it may or may not reduce performance.

In detail

Detected with distribution comparisons such as PSI or the KS statistic against a reference window. It differs from concept drift, where the relationship between inputs and outcome changes while inputs may look the same. Input drift is an early indicator, not proof of harm: confirm with matured outcomes.