Analyzing and Improving Coherence of Large Language Models in Question Answering

Ivano Lauriola, Stefano Campese, Alessandro Moschitti

Abstract: Large language models (LLMs) have recently revolutionized natural language processing. These models, however, often suffer from instability or lack of coherence, that is the ability of the models to generate semantically equivalent outputs when receiving diverse yet semantically equivalent input variations. In this work, we analyze the behavior of multiple LLMs, including Mixtral-8x7B, Llama2-70b, Smaug-72b, and Phi-3, when dealing with multiple lexical variations of the same info-seeking questions. Our results suggest that various LLMs struggle to consistently answer diverse equivalent queries. To address this issue, we show how redundant information encoded as a prompt can increase the coherence of these models. In addition, we introduce a Retrieval-Augmented Generation (RAG) technique that supplements LLMs with the top-k most similar questions from a question retrieval engine. This knowledge-augmentation leads to 4-8 percentage point improvement in end-to-end performance in factual question answering tasks. These findings underscore the need to enhance LLM stability and coherence through semantic awareness.