ChronoBias: A Benchmark for Evaluating Time-conditional Group Bias in the Time-sensitive Knowledge of Large Language Models

Abstract

In this paper, we propose ChronoBias , a novel benchmark for evaluating time-conditional group bias in the time-sensitive knowledge of large language models (LLMs).Our benchmark is constructed via a template-based semi-automated generation method, balancing the quality-quantity trade-off in existing benchmark curation approaches.For knowledge that changes over time, time-conditional group bias exhibits varying patterns across time intervals, evident in both the best- and worst-performing groups and in the bias metric itself.In addition to parametric knowledge bias –which influences group bias across all time intervals–we identify time-sensitivity bias as an additional factor after a model’s knowledge cutoff, accounting for much of the variation in time-conditional group bias over time.Since both biases are irreducible, retrieval-augmented generation (RAG) can be a promising approach, as it can address post-cutoff knowledge and better leverage pretraining knowledge that is underrepresented in the model parameters.While RAG improves both overall performance and group bias, we observe that the disparate patterns of time-conditional group bias still persist.Therefore, through extensive experiments with various model configurations, we illustrate how accurate and fair RAG-based LLMs should behave and provide actionable guidelines toward constructing such ideal models.