KAISEN: Reproducible Subgroup Fairness Auditing for Clinical Risk Models

TL;DR - KAISEN is a reproducible, five-phase framework for auditing subgroup fairness in clinical risk models. Synthetic stress tests show that mitigation, diagnostics, and drift-monitoring components can fail unpredictably or silently.

• Per-group threshold optimization reduced equalized-odds disparity in all 48 held-out runs.
• Group-wise Platt scaling improved calibration but had inconsistent, near-zero average effects on fairness.
• Mechanism diagnostics identified all controlled cases but missed every model-driven case under proxy misspecification without warning.
• CUSUM drift thresholds transferred poorly across cohort realizations; the synthetic results do not establish clinical validity.