Hallucination-Free?: legal RAG hallucination rates

The paper Hallucination-Free? Assessing the Reliability of Leading AI Legal Research Tools, published in the Journal of Empirical Legal Studies, tests three commercial legal research tools: Lexis+ AI, Westlaw AI-Assisted Research and Ask Practical Law AI. The study was preregistered; the authors wrote legal queries, verified claims and citations, and distinguished a hallucination, a factual error and a substantive answer. Despite RAG and access to databases, the systems hallucinated in 17-33% of answers. That is lower than general-purpose GPT-4 but does not confirm the vendors’ claims of reliability. A separate finding: a refusal or an evasive answer lowers the hallucination rate without making the product more useful. For the Lexometrica leaderboard this is grounds to treat citation accuracy, content accuracy and the share of answered queries as different metrics.