Expanding a Credit-Risk Model to a New Score Band
Scenario
Your current probability-of-default (PD) lending model was trained only on applicants with credit scores ≥ 650 because those were historically considered for lending. Management now wants to evaluate and potentially lend to applicants with scores < 650.
Question
How would you leverage the existing model and available data to score the < 650 population, while addressing dataset shift and selection bias? Outline a practical plan that:
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Diagnoses distribution/selection shift between ≥ 650 and < 650 populations.
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Reuses and adapts the existing model instead of training from scratch.
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Obtains or infers labels and/or corrects bias for the previously unserved group (< 650).
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Imposes reasonable inductive biases (e.g., monotonic constraints) to reduce risky extrapolation.
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Validates, calibrates, and proposes a safe rollout to production.
Hints: covariate/selection shift, importance weighting, reject inference, semi-supervised learning, synthetic augmentation, boundary expansion, monotonic constraints, and conservative calibration.