CIV-DG: Conditional Instrumental Variables for Domain Generalization in Medical Imaging

Shaojin Bai; Yuting Su; Weizhi Nie

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arXiv · 2603.25202

CIV-DG: Conditional Instrumental Variables for Domain Generalization in Medical Imaging

Shaojin Bai·Yuting Su·Weizhi Nie

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Abstract

Cross-site generalizability in medical AI is fundamentally compromised by selection bias, a structural mechanism where patient demographics (e.g., age, severity) non-randomly dictate hospital assignment. Conventional Domain Generalization (DG) paradigms, which predominantly target image-level distribution shifts, fail to address the resulting spurious correlations between site-specific variations and diagnostic labels. To surmount this identifiability barrier, we propose CIV-DG, a causal framework that leverages Conditional Instrumental Variables to disentangle pathological semantics from scanner-induced artifacts. By relaxing the strict random assignment assumption of standard IV methods, CIV-DG accommodates complex clinical scenarios where hospital selection is endogenously driven by patient demographics. We instantiate this theory via a Deep Generalized Method of Moments (DeepGMM) architecture, employing a conditional critic to minimize moment violations and enforce instrument-error orthogonality within demographic strata. Extensive experiments on the Camelyon17 benchmark and large-scale Chest X-Ray datasets demonstrate that CIV-DG significantly outperforms leading baselines, validating the efficacy of conditional causal mechanisms in resolving structural confounding for robust medical AI.

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BibTeX RIS

Shaojin Bai, Yuting Su, Weizhi Nie. 2026-03-26. CIV-DG: Conditional Instrumental Variables for Domain Generalization in Medical Imaging. https://arxiv.org/abs/2603.25202

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