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Multi-Agent Debate for LLM Judges with Adaptive Stability Detection
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Proposes a multi-agent debate framework for LLM judges with a time-varying Beta-Binomial mixture model and KS-test-based adaptive stopping, reporting accuracy gains over majority voting on six judging benchmarks.
Problem
LLM-as-judge ensembles typically aggregate independent judgments via static methods like majority voting, which can fail even when individual agents are correct; iterative debate is also costly without a principled stopping rule.
Approach
Models debate as Bayesian belief updating over latent concepts, proves debate improves over majority vote under assumptions, and tracks the judge-correctness distribution with a time-varying two-component Beta-Binomial mixture fit by EM, halting when KS distance between consecutive rounds stays below 0.05 for two rounds.
Key results
- Debate with 7 agents improves over majority voting (SoM) on LLMBar for Gemini-2.0-Flash, from 77.75% to 81.83%.
- On JudgeBench, Gemini-2.0-Flash debate reaches 68.06% versus 66.13% for SoM and 63.66% for single sampling.
- Debate underperforms SoM on BIG-Bench for Qwen-2.5-7B (72.20% vs 76.60%) and Llama-3.1-8B (74.00% vs 81.80%), so gains are not uniform.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Replace majority voting with iterative Debate | Gemini-2.0-Flash judge ensemble · BIG-Bench | accuracy: 81.50 ± 2.41 -> 82.30 ± 2.36 | Helped |
| Replace majority voting with iterative Debate | Gemini-2.0-Flash judge ensemble · JudgeBench | accuracy: 66.13 ± 3.72 -> 68.06 ± 3.66 | Helped |
| Replace majority voting with iterative Debate | Gemini-2.0-Flash judge ensemble · LLMBar | accuracy: 77.75 ± 2.35 -> 81.83 ± 2.18 | Helped |
| Replace majority voting with iterative Debate | Gemini-2.0-Flash judge ensemble · TruthfulQA | accuracy: 72.01 ± 3.10 -> 74.30 ± 2.99 | Helped |
| Replace majority voting with iterative Debate | Gemini-2.0-Flash judge ensemble · MLLM-Judge | accuracy: 68.00 ± 3.23 -> 69.25 ± 3.19 | Helped |
| Replace majority voting with iterative Debate | Gemini-2.0-Flash judge ensemble · JudgeAnything | accuracy: 83.46 ± 6.30 -> 85.71 ± 5.95 | Helped |
| Use adaptive KS stopping instead of fixed 3-round debate | Gemini-2.0-Flash judge ensemble · BIG-Bench | accuracy: 81.40 -> 81.70 | Helped |
| Use adaptive KS stopping instead of fixed 3-round debate | Gemini-2.0-Flash judge ensemble · JudgeBench | accuracy: 67.60 -> 67.74 | Helped |
| Use adaptive KS stopping instead of fixed 3-round debate | Gemini-2.0-Flash judge ensemble · LLMBar | accuracy: 81.30 -> 81.33 | Helped |
| Use adaptive KS stopping instead of fixed 3-round debate | Gemini-2.0-Flash judge ensemble · TruthfulQA | accuracy: 73.40 -> 73.81 | Helped |
| Use adaptive KS stopping instead of fixed 3-round debate | Gemini-2.0-Flash judge ensemble · MLLM-Judge | accuracy: 68.20 -> 68.63 | Helped |
| Use adaptive KS stopping instead of fixed 3-round debate | Gemini-2.0-Flash judge ensemble · JudgeAnything | accuracy: 85.10 -> 85.71 | Helped |
Surprising findings
- Debate underperforms majority voting on BIG-Bench for Qwen-2.5-7B and Llama-3.1-8B, contrary to the framing that debate generally helps.
- Diversity pruning did not improve accuracy as claimed in prior work, which the authors attribute to limited answer spaces in judgment tasks.
Limitations
- Theoretical guarantees rely on strong assumptions (conditional independence, true-concept predictiveness) and the proof's inequalities are loosely justified with epsilon terms.
- Debate gains are inconsistent across models and datasets, and debate underperforms majority voting on several benchmarks.
- Small evaluation subsets (e.g., 180 JudgeAnything entries, sampled 1,000 MLLM-Judge) and large standard errors limit statistical confidence in reported gains.
Experimental setup
Datasets: BIG-Bench sports understanding JudgeBench LLMBar TruthfulQA MLLM-Judge JudgeAnything
Benchmarks: BIG-Bench sports understanding JudgeBench LLMBar TruthfulQA MLLM-Judge JudgeAnything
Metrics: accuracy standard error rounds until stopping
Baselines: Single model SoM (majority vote) MAD RECONCILE
Builds on: LLM-as-a-Judge Multi-agent debate Self-consistency RECONCILE
Closest papers by meaning
- Debate or Vote: Which Yields Better Decisions in Multi-Agent Large Language Models? (NeurIPS 2025 · similarity 0.90)
- When Debate Helps: Proposal Supply and Verification-Aware Readout in Multi-Agent Reasoning (NeurIPS 2026 · similarity 0.90)
- Multi-LLM Debate: Framework, Principals, and Interventions (NeurIPS 2024 · similarity 0.90)
- Efficient Multi-Agent Reasoning via Confidence-Guided Adaptive Debate (ICML 2026 · similarity 0.90)
- Should we be going MAD? A Look at Multi-Agent Debate Strategies for LLMs (ICML 2024 · similarity 0.89)
- The Value of Variance: Mitigating Debate Collapse in Multi-Agent Systems via Uncertainty-Driven Policy Optimization (ICML 2026 · similarity 0.89)
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