Trust-weighted average of AI judges stays accurate on small evaluation sets

A method using item-response theory learns judge reliability from all items jointly and outperforms standard aggregation when reference sets are under a few hundred items.

Academic
Junhyung Ahn

University of Illinois Urbana-Champaign

Research Digest··2 min read

In one line

AGORA aggregates LLM judges by weighting each judge's reliability, outperforming equal-weight averaging and confusion-table models on small evaluation sets.

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Evaluating AI systems often requires human judges, but that is expensive. A common cheaper alternative is using several large language models (LLMs), or "LLM judges," to score items, then averaging their scores. However, this average gives equal weight to weak and strong judges, and other statistical methods need too many data points to learn which judges are reliable.

This paper introduces AGORA, a method that treats each scored item as having a hidden quality. AGORA learns a "reliability weight" for each judge, how steeply its scores track that hidden quality, so unreliable judges are down-weighted. It also models how each judge uses the rating scale, using fewer parameters than older methods.

On three benchmarks, AGORA matched or beat existing methods on large evaluation sets. Its advantage grew as sets shrank, outperforming a standard method (Dawid-Skene) on 98–100% of random five-judge pools with just 50 items. A new statistic can predict, without human labels, when this trust-weighting helps.

How it works

before and after
STANDARD AGGREGATION (E.G., PER-ITEMJudge ratings: Scores from LLMsJudge ratingsScores from LLMsSimple average: Per-item meanSimple averagePer-item meanAGORA (THIS WORK)discretizedratingsquality &sensitivityJudge ratings: Scores from LLMsJudge ratingsScores from LLMsIRT model: Graded-response + horseshoeIRT modelGraded-response +horseshoeTrust-weighted rating: Downweights unreliable judgesTrust-weightedratingDownweights unreliablejudgesAgreement dispersion statistic predicts gain without human labels.
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