Revisiting the Self-Consistency Challenges in Multi-Choice Question Formats for Large Language Model Evaluation

Abstract

Multi-choice questions (MCQ) are a common method for assessing the world knowledge of large language models (LLMs), demonstrated by benchmarks such as MMLU and C-Eval. However, recent findings indicate that even top-tier LLMs, such as ChatGPT and GPT4, might display inconsistencies when faced with slightly varied inputs. This raises concerns about the credibility of MCQ-based evaluations. To address this issue, we introduced three knowledge-equivalent question variants: option position shuffle, option label replacement, and conversion to a True/False format. We rigorously tested a range of LLMs, varying in model size (from 6B to 70B) and types—pretrained language model (PLM), supervised fine-tuning (SFT), and reinforcement learning from human feedback (RLHF). Our findings from MMLU and C-Eval revealed that accuracy for individual questions lacks robustness, particularly in smaller models (<30B) and PLMs. Consequently, we advocate that consistent accuracy may serve as a more reliable metric for evaluating and ranking LLMs.