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A Counterfactual Diagnostic Framework for Explaining KS Deterioration in Credit Risk Model Validation

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  • Yiqing Wang

Abstract

The Kolmogorov-Smirnov (KS) statistic is widely used in credit risk model monitoring and validation to assess discriminatory power. In practice, a material decline in KS often triggers governance review and requires validation teams to identify the breach source and the potential business risk. However, such diagnosis is frequently conducted on an ad hoc basis, relying on the judgment of individual validators rather than a standardized analytical framework. This paper proposes a counterfactual diagnostic framework for explaining KS deterioration in credit risk model validation. The framework sequentially attributes observed KS decline to sampling variability, portfolio composition change, covariate shift, and residual deterioration consistent with model drift, with explicit gateway conditions governing escalation at each stage. Simulation experiments demonstrate that the proposed approach provides more interpretable and governance-relevant explanations than threshold-based review alone, and contributes to more consistent, transparent, and defensible performance-breach assessment in credit risk model validation.

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  • Yiqing Wang, 2026. "A Counterfactual Diagnostic Framework for Explaining KS Deterioration in Credit Risk Model Validation," Papers 2604.11561, arXiv.org.
    • Handle: RePEc:arx:papers:2604.11561
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    References listed on IDEAS

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    1. Anderson, Raymond, 2007. "The Credit Scoring Toolkit: Theory and Practice for Retail Credit Risk Management and Decision Automation," OUP Catalogue, Oxford University Press, number 9780199226405.
    2. Masashi Sugiyama & Taiji Suzuki & Shinichi Nakajima & Hisashi Kashima & Paul Bünau & Motoaki Kawanabe, 2008. "Direct importance estimation for covariate shift adaptation," Annals of the Institute of Statistical Mathematics, Springer;The Institute of Statistical Mathematics, vol. 60(4), pages 699-746, December.
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