LM vs LM: Detecting Factual Errors via Cross Examination
Paper · 2023 · Roi Cohen, May Hamri, Mor Geva et al.
Summary
Language models often state false facts with confidence, and these errors are hard to catch automatically. Cohen et al. present LM vs LM, a zero-shot approach to detecting factual errors that borrows the idea of cross-examination from legal practice. The intuition is that a model asserting something false will tend to contradict itself when probed from several angles. One LM, the EXAMINER, questions another LM, the EXAMINEE, about a claim the EXAMINEE produced. In practice both roles can be the same model with different prompts. The process has three stages. First, the examiner proposes initial questions. Next, it asks follow-up questions for up to five turns. Finally, it labels the claim "correct" or "incorrect." No reference documents or external knowledge bases are required. The authors evaluated the method on factual question-answering claims from ChatGPT, GPT-3 and LLaMA across four benchmarks. It flagged more than 70% of false claims while keeping precision above 80%, often well ahead of existing baselines. The work suggests that interaction between models can expose hallucinations without supervision.
Key points
- Three-stage protocol. The stages are setup, iterative follow-ups (capped at five turns) and a binary verdict. Any output that is not a clear verdict counts as rejecting the claim.
- Overall results. Across datasets and settings, recall exceeds 70% and precision exceeds 80%. With GPT-3 as EXAMINER and a retrieval-augmented GPT-3 as EXAMINEE, the scores were P 87.5, R 75.7 and F1 80.3.
- Examination length. Examiners ask about 6–7 questions per examination, usually with 1–2 rounds of follow-ups.
- Examiner strategies. A manual review of 96 examinations identified several strategies:
- paraphrasing the claim (about 60% of examinations);
- re-asking earlier questions in new wording (about half);
- checking implied consequences of the claim;
- requesting supporting evidence (about 30%);
- breaking the claim into sub-questions. ChatGPT did this in about 75% of examinations versus 10% for GPT-3, which may explain ChatGPT's stronger performance.
- Limitations. The method requires many API calls and relies on large, instruction-following models (over 10B parameters). It tends to fail when the examinee holds a set of false beliefs that are consistent with one another.
Institutions
📚 Shelves 6 Computer Science · 9,086 works Artificial Intelligence · 8,889 works Arts and Humanities · 9,296 works Language and Linguistics · 9,206 works Social Sciences · 744 works Sociology and Political Science · 221 works
Cite
Cite as Roi Cohen, May Hamri, Mor Geva and Amir Globerson. 2023. LM vs LM: Detecting Factual Errors via Cross Examination. Proceedings of the 2023 Conference on Empirical Methods in Natural Language Processing.
@inproceedings{cohen2023lm,
title = {{LM vs LM: Detecting Factual Errors via Cross Examination}},
author = {Roi Cohen, May Hamri, Mor Geva and Amir Globerson},
booktitle = {Proceedings of the 2023 Conference on Empirical Methods in Natural Language Processing},
year = {2023},
doi = {10.18653/v1/2023.emnlp-main.778},
url = {https://doi.org/10.18653/v1/2023.emnlp-main.778}
}References
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