GreekBarBench: A Challenging Benchmark for Free-Text Legal Reasoning and Citations

2025-05-22

AI Summary

This study addresses the challenge of evaluating large language models’ (LLMs) legal reasoning and statutory/case-law citation capabilities on the Greek Bar Examination—a task lacking dedicated benchmarks. We introduce the first free-text legal reasoning benchmark for this examination, covering five core domains: constitutional, civil, criminal, administrative, and procedural law. Methodologically, we propose a three-dimensional scoring scheme and an “LLM-as-a-judge” automated evaluation framework, validated via a meta-evaluation benchmark to assess adjudicator consistency. We find that concise, snippet-based scoring rules significantly improve agreement between LLM judges and human experts (Cohen’s κ = 0.82). Our system integrates citation localization, multi-dimensional automated scoring, and calibration mechanisms to evaluate 13 state-of-the-art LLMs. The top-performing model exceeds the human expert mean score but falls short of the top 5% percentile, revealing critical limitations in rigorous legal citation and logically closed reasoning.

Technology Category

• Machine Learning: Large Multimodal Models (LMMs)
• Natural Language Processing: Interpretability, Analysis, and Evaluation of NLP Models
• Knowledge Representation and Reasoning: Computational Complexity of Reasoning

Application Category

• Search and Retrieval-Augmented AI: Web evaluation methodologies and metrics
• Economics, Online Markets and Human Computation: Cost models of using LLMs in production systems
• Semantics and Knowledge: Data modeling to support human-machine intelligence, including LLMs agents, intelligent system behavior, explanations, and user-friendly interactions

Abstract

We introduce GreekBarBench, a benchmark that evaluates LLMs on legal questions across five different legal areas from the Greek Bar exams, requiring citations to statutory articles and case facts. To tackle the challenges of free-text evaluation, we propose a three-dimensional scoring system combined with an LLM-as-a-judge approach. We also develop a meta-evaluation benchmark to assess the correlation between LLM-judges and human expert evaluations, revealing that simple, span-based rubrics improve their alignment. Our systematic evaluation of 13 proprietary and open-weight LLMs shows that even though the best models outperform average expert scores, they fall short of the 95th percentile of experts.

Problem

• Evaluates LLMs on Greek Bar exam legal questions with citations
• Proposes 3D scoring and LLM-as-judge for free-text evaluation
• Assesses LLM-judge and human expert evaluation alignment

Innovation

• Three-dimensional scoring system for evaluation
• LLM-as-a-judge approach for assessment
• Meta-evaluation benchmark for alignment improvement