Calibrating LLM-as-a-Judge for Argument Quality Assessment through Prompting and Scoring Scale Design

Guilherme Aren Marchetti, Gil Rocha, Henrique Lopes Cardoso


Abstract
Although LLM-as-a-Judge approaches have been successful in several domains, recent studies show that LLMs still struggle with Computational Argumentation tasks, particularly Argument Quality Assessment. Motivated by recent results in Information Retrieval showing that scoring granularity can affect the effectiveness of LLM-based document rankers, this paper investigates whether the same effect holds in Argument Quality Assessment scenarios.

Our results demonstrate that, in several cases, more granular scoring ranges yield substantially higher agreement after mapping predictions back to the original scale. This contrasts with how humans evaluate, where reducing the granularity of possible scores can foster clearer, more consistent decisions. Additionally, our error analysis reveals a recurring limitation: LLMs tend to underestimate arguments labeled by human experts as high quality, frequently assigning them medium scores instead. This suggests that, despite the gains obtained through prompt and scale design, current LLMs remain poorly calibrated at the upper end of the argument quality scale.
Anthology ID:
2026.luhme-1.16
Volume:
Proceedings of the 3rd Workshop on Language Understanding in the Human-Machine Era (LUHME 2026)
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Rui Sousa-Silva, Henrique Lopes Cardoso, Maarit Koponen, Antonio Pareja-Lora
Venues:
LUHME | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
197–214
Language:
URL:
https://aclanthology.org/2026.luhme-1.16/
DOI:
Bibkey:
Cite (ACL):
Guilherme Aren Marchetti, Gil Rocha, and Henrique Lopes Cardoso. 2026. Calibrating LLM-as-a-Judge for Argument Quality Assessment through Prompting and Scoring Scale Design. In Proceedings of the 3rd Workshop on Language Understanding in the Human-Machine Era (LUHME 2026), pages 197–214, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Calibrating LLM-as-a-Judge for Argument Quality Assessment through Prompting and Scoring Scale Design (Marchetti et al., LUHME 2026)
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PDF:
https://aclanthology.org/2026.luhme-1.16.pdf