An Experimental Assessment of AI-Based Legal Decision-Making Systems in Contract Analysis and Risk Detection

Abstract

This comprehensive experimental study evaluates the performance, reliability, and practical applicability of AI-based legal decision-making systems in contract analysis and risk detection. Utilizing a corpus of 5,247 contracts with expert-validated annotations from 12 legal professionals, we benchmark four classes of AI systems—rule-based, supervised machine learning (XGBoost), fine-tuned transformer models (Legal-BERT), and large language models (GPT-4, Claude 3)—across multiple dimensions critical to legal practice. The Key Findings of this research : a) Performance Variability: Fine-tuned Legal-BERT achieved the highest overall clause classification F1-score (0.923, 95% CI [0.917, 0.929]), but exhibited significant degradation in cross-jurisdictional applications (28.4% performance drop from US to UK contracts). b) Risk Detection Gaps: All systems demonstrated decreasing recall with increasing risk severity. GPT-4 missed 18.2% of high-severity risks (severity ≥4), while Legal-BERT missed 12.3% of total risk severity weight (FNRP metric). c)Decision Inconsistency: LLMs showed substantial inconsistency, with GPT-4 achieving only 0.81 intra-model Jaccard similarity across identical inputs and 14.7% decision variation on identical clause phrasings. d)Domain-Specific Performance: Rule-based systems performed adequately on standardized agreements (NDA: F1=0.812) but failed catastrophically on complex contracts (M&A: F1=0.432). e) Cost-Effectiveness: Local fine-tuned models provided 92.3% of GPT-4's performance at 3.5% of the cost ($0.0087 vs $0.2478 per document).We introduce two novel legal-specific metrics—False-Negative Risk Penalty (FNRP) and Severity-Weighted F1 (SwF1)—that better capture the asymmetric cost structure of legal errors. Based on our empirical findings, we propose a three-tier human-in-the-loop deployment framework that reduces attorney review time by 64% while maintaining 99.7% risk coverage. The study establishes evidence-based performance thresholds for safe deployment, recommending against autonomous use of any system with FNRP > 0.15 or cross-jurisdiction performance degradation > 25%. Our findings challenge optimistic claims of AI autonomy in legal decision-making and provide a rigorous, reproducible framework for evaluating legal AI systems in practice.

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