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Exploiting Primacy Effect to Improve Large Language Models (arxiv.org)
1 point by hdvr on Jul 21, 2025 | hide | past | pdf | discuss on HN

In plain words: Fine-tuning makes language models lean harder toward picking the first answer choice, so the fix puts the option most similar to the question first. That simple reordering, done without knowing the right answer, raised multiple-choice accuracy compared with leaving options in their original order.

Abstract · Exploiting Primacy Effect To Improve Large Language Models

Large Language Models (LLMs) have become essential in many Natural Language Processing (NLP) tasks, leveraging extensive pre-training and fine-tuning to achieve high accuracy. However, like humans, LLMs exhibit biases, particularly positional biases such as primacy and recency effects, which can influence the accuracy of the answers. The primacy effect-where items presented first are more likely to be remembered or selected-plays a key role in Multiple Choice Question Answering (MCQA), where the order of answer options can affect prediction outcomes. This study focuses on primacy bias in fine-tuned LLMs: We first show that fine-tuning amplifies this bias, probably due to exposure to human-like patterns. Hence, we strategically leverage this effect by reordering response options based on semantic similarity to the query, without requiring knowledge of the correct answer. Our experimental results show that this approach significantly improves performance in MCQA. More generally, our findings underscore the dual nature of biases as both challenges and opportunities, offering insights for bias-aware model design and NLP applications.

Bianca Raimondi, Maurizio Gabbrielli
arXiv:2507.13949 · cs.CL, cs.AI · submitted Jul 18, 2025
abstract · pdf · html · Accepted by RANLP 2025

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