What Is Population Stability Index (PSI)?

Population Stability Index (PSI)

Population Stability Index looks at the magnitude which a variable has changed or shifted in distribution between two samples over the course of a given time. PSI is calculated as: PSI = (% Actual – % Expected) x ln(% Actual / % Expected)

The larger the PSI, the less similar your distributions are, which allows you to set up thresholding alerts on the drift in your distributions. PSI is a great metric for both numeric and categorical features where distributions are fairly stable.

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