Decomposing LLM-Judge–Human Agreement: How Much Is Inherited Surface Preference?

Gaurav Kumar


Abstract
LLM-as-judge evaluation is typically validated using judge-human agreement with standard benchmarks reporting agreement rates of roughly 80-85 %. We show that this aggregate metric can be misleading. Most of that agreement comes from pairs where both judge and human prefer the longer, better-formatted response, rather than from agreement on response quality. On the remaining pairs, agreement drops to chance levels on MT-Bench, and below chance when surface cues mislead. We show this with two simple logistic-regression baselines on length, structure, and lexical features: one predicts the human’s pick, one predicts the judge’s. The pattern holds across closed and open judges and both benchmarks, and is strongest on the expert annotations the field treats as the quality gold standard. We suggest reporting the inheritance share alongside aggregate agreement: a simple reporting metric we defined that shows whether a judge agrees with humans for the right reasons.
Anthology ID:
2026.insights-1.7
Volume:
Proceedings of the Seventh Workshop on Insights from Negative Results in NLP
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
João Sedoc, Raphael Shu, Aleksandr Drozd, Arjun Akula, Anna Rogers, Salvatore Giorgi, Adrian Benton
Venues:
insights | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
60–69
Language:
URL:
https://aclanthology.org/2026.insights-1.7/
DOI:
Bibkey:
Cite (ACL):
Gaurav Kumar. 2026. Decomposing LLM-Judge–Human Agreement: How Much Is Inherited Surface Preference?. In Proceedings of the Seventh Workshop on Insights from Negative Results in NLP, pages 60–69, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Decomposing LLM-Judge–Human Agreement: How Much Is Inherited Surface Preference? (Kumar, insights 2026)
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https://aclanthology.org/2026.insights-1.7.pdf
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