Clinical NLI abstention gate¶

The clinical NLI gate is a local, deterministic policy boundary for evidence links. It consumes calibrated entailment, contradiction, and neutral probabilities. It emits entailment or contradiction only when the winning class clears its calibrated threshold and has the configured margin over the next-best class. Everything else becomes abstain.

An abstention is an explicit handoff to human review. It is not a negative clinical conclusion, and the gate never makes a diagnosis, treatment decision, or autonomous clinical judgment.

Example¶

from openmed.clinical.nli_gate import EvidenceLink, NLIThresholds, evaluate_nli

evidence = EvidenceLink.from_text(
    source_id="synthetic-note-1",
    claim_id="synthetic-claim-1",
    source_text="Synthetic evidence supports the synthetic claim.",
    claim_text="The synthetic claim is supported.",
    start=0,
    end=48,
)

result = evaluate_nli(
    {
        "entailment": 0.96,
        "contradiction": 0.02,
        "neutral": 0.02,
        "calibration_id": "synthetic-calibration-v1",
    },
    evidence,
    thresholds=NLIThresholds(
        entailment=0.90,
        contradiction=0.90,
        margin=0.10,
        calibration_id="synthetic-calibration-v1",
    ),
)

assert result.outcome == "entailment"
assert result.autonomous_decision is False

For an ambiguous or neutral score, result.outcome is "abstain", result.requires_human_review is True, and result.human_review contains a queue-safe reason plus the typed evidence link. The result and audit entry contain offsets, hashes, score metadata, and provenance only; premise, hypothesis, and source text are never retained.

NLIThresholds.calibration_id identifies the held-out calibration artifact that selected the operating point. A score set carrying a different calibration ID is rejected rather than silently compared with the wrong thresholds. The module performs no model download or mandatory network call.

This is an assistive safety boundary. It does not provide a compliance certification or a clinical decision guarantee.