Do LLMs Know What They Know? Measuring Metacognitive Efficiency with Signal Detection Theory

arXiv cs.CL / 3/27/2026

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Key Points

  • The paper argues that common LLM confidence calibration metrics (e.g., ECE, Brier score) mix two abilities—Type-1 sensitivity (how much the model knows) and Type-2 metacognitive sensitivity (how well it knows what it knows).
  • It proposes an evaluation framework using Type-2 Signal Detection Theory, introducing meta-d' and an M-ratio to separately measure metacognitive capacity and metacognitive efficiency.
  • Experiments on four LLMs across 224,000 factual QA trials show large differences in metacognitive efficiency even when Type-1 sensitivity is similar, including cases where a model ranks highest by d' but lowest by M-ratio.
  • The study finds metacognitive efficiency is domain-specific and can be shifted by temperature changes, indicating that confidence policy (Type-2 criterion) can move independently of underlying metacognitive capacity for some models.
  • It reports that AUROC_2 and M-ratio can produce fully inverted model rankings, suggesting these metrics answer fundamentally different evaluation questions, with implications for model selection and deployment.

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