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Population stability index

As explained in Financial AI in Practice

The population stability index quantifies changes between distributions of a variable or model population across time or samples.

The population stability index (PSI) is a credit-scoring metric for monitoring drift in applicant populations. It helps flag shifts associated with changing customer demographics or economic conditions. section 4.4 section 4.4.1

PSI complements AUC and K-S: those metrics assess a model’s ability to distinguish good from bad borrowers, while PSI flags changes in the population. section 4.4.1

How Financial AI in Practice covers it

How deep it goes
Identifies PSI as a drift-monitoring metric but does not specify its calculation, thresholds, or response procedure.
Examples
Flags applicant-population shifts associated with changing customer demographics or economic conditions.
What you can do after
Diagnose potential population drift by using PSI to flag changes in credit applicants.
How it connects
Pairs PSI with AUC and K-S as core credit-risk metrics, distinguishing drift monitoring from borrower discrimination.

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