LBR: An Innovative Method to Mitigate Length Bias of Large Language Models in Recommendation Systems

This article introduces the LBR (Length Bias Reduction) method, an innovative solution to the length bias problem of large language models (LLMs) in recommendation systems. With the widespread application of LLMs in the recommendation field, length bias (the model's tendency to select candidate items with longer text) significantly affects recommendation quality. The LBR method aims to mitigate this challenge, and we will discuss its core mechanisms, experimental validation, and practical application value.

Length bias refers to the systematic influence of the description text length on the scoring of candidate items by large language models in recommendation scenarios. Specifically, when comparing two items with similar content quality but different lengths, the model tends to give a higher relevance score to the one with a longer description. This bias stems from the LLM's preference for text richness during pre-training, but it may lead to suboptimal ranking results in recommendation tasks.

LBR mitigates length bias through multi-dimensional strategies:

1. Length-aware Data Augmentation: A length-balanced sampling strategy is introduced during training to ensure the model is exposed to samples with different length distributions, avoiding over-adaptation to long-text patterns.

2. Bias-aware Loss Function: A dedicated regularization term is designed to explicitly penalize the model's sensitivity to text length, encouraging it to focus on content quality rather than length.

3. Contrastive Learning Framework: Length contrast sample pairs are constructed to train the model to recognize the equivalence of the same semantics expressed in different lengths, enhancing length invariance.

LBR was validated on public recommendation datasets such as Toy, Office, and Book:

• The NDCG@10 metric was significantly improved compared to baseline LLM recommendation methods
• The recall rate of short-text items was significantly improved, and the recommendation results were more balanced
• User satisfaction metrics showed an increase in recommendation diversity

The code is based on the Python ecosystem, uses uv for dependency management, and supports a configuration file-driven training process.

LBR provides a deployable solution for recommendation system developers in the industry:

• E-commerce Platforms: Balance exposure opportunities between long-tail and popular products
• Content Platforms: Ensure fair recommendations for short and long videos
• Recruitment Systems: Avoid the impact of job description length on talent matching quality

LBR provides important improvements to the fairness and effectiveness of LLMs in recommendation systems. As LLMs are deeply applied in the recommendation field, solving structural problems such as length bias is key to enhancing user experience. This open-source implementation provides valuable practical references for researchers and engineers.