arXiv — Machine Learning · · 4 min read

Counterfactual Evaluation Reveals Hidden Capability Profiles in Clinical LLMs and Agents

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Computer Science > Machine Learning

arXiv:2605.30590 (cs)
[Submitted on 28 May 2026]

Title:Counterfactual Evaluation Reveals Hidden Capability Profiles in Clinical LLMs and Agents

Authors:Matt Turk
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Abstract:Two clinical AI systems can score nearly identically on coverage-based rubrics yet behave radically differently when their patient inputs change: one updates its recommendations to match the new clinical signal, while the other produces the same output regardless. We introduce the Causal Sensitivity Score (CSS), a pre-registered interventional metric that mutates oncology tumor-board cases along five clinically meaningful dimensions - biomarker flips, prior-treatment failures, biomarker removals, surgery-status changes, and stage perturbations - and scores whether each model updates its recommendations in the pre-registered correct direction using a {0, 0.5, 1.0} scale. Benchmarked against the Consensus Match Score (CMS), a coverage-based weighted recall metric, six frontier models from three labs evaluated in single-shot inference across 224 cases rank in nearly opposite orders: all six models change rank, the CMS-worst model becomes CSS-best, and one upper-mid CMS model ranks last on CSS. We further surface a universal safety blind spot: every frontier model fails on surgery-status interventions (at most 17.2% CSS on Family D), a finding CMS does not expose. The metric also transfers to tool-using agents: in a ReAct-style experiment, tool use improves CSS for five of six models (+2.5 to +20.3 percentage points), yet the lowest-CSS model retrieves the same chart sections and still fails to update its recommendations - revealing a structural responsiveness deficit visible only under counterfactual evaluation. Cross-judge replication and three-rater medical-professional validation confirm the aggregate findings. Interventional pre-registered metrics like CSS complement coverage-based evaluation for clinical AI agents: they capture responsiveness that coverage metrics miss and offer a candidate dense reward signal for future agentic RL systems.
Comments: Accepted to RLEval @ ACM CAIS 2026 (Workshop on Methods and RL Environments for Evaluating AI Agents) and selected for an invited talk based on reviewer ratings. 4-page short paper + appendix
Subjects: Machine Learning (cs.LG); Artificial Intelligence (cs.AI); Computation and Language (cs.CL)
Cite as: arXiv:2605.30590 [cs.LG]
  (or arXiv:2605.30590v1 [cs.LG] for this version)
  https://doi.org/10.48550/arXiv.2605.30590
arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Matthew Turk [view email]
[v1] Thu, 28 May 2026 21:37:06 UTC (1,458 KB)
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