Retrieving Facts or Reinforcing Beliefs? Towards Understanding Confirmation Bias in RAG Systems for Scientific Claim Verification

Qile Wan, Davide Venditti, Fabio Massimo Zanzotto, Iryna Gurevych, Lizhen Qu


Abstract
The rapid growth of scientific literature has made automated verification of scientific claims increasingly important, with Retrieval-Augmented Generation (RAG) systems emerging as a promising solution. However, their multi-stage architecture raises concerns about confirmation bias, where systems preferentially retrieve and generate evidence that supports a given claim. In this paper, we present CoBiT (Confirmation Bias Test), the first benchmark for systematically evaluating confirmation bias in RAG systems, consisting of 707 minimally perturbed claim–counterclaim pairs. We propose a unified framework with stage-specific metrics to quantify bias in both re-ranking and generation, including Ranking Bias Magnitude (RBM), Confirmation Bias Rate (CBR), and consistency measures. Our experiments on OpenScholar,ScholarQA, and LLM baselines reveal that confirmation bias arises at different stages of the RAG pipeline and can be amplified by re-ranking and generation. In particular, SciRAG achieves the lowest generation bias (CBR = 0.13), it exhibits higher bias in re-ranking, and OpenScholar shows the greatest inconsistency between claims and counterclaims. These findings highlight the need for fine-grained evaluation of epistemic risks in RAG systems and provide practical tools for diagnosing confirmation bias.

Code and Data https://github.com/Presence76/Confirmation_bias_evaluation
Anthology ID:
2026.emnlp-main.44
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
958–974
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URL:
https://aclanthology.org/2026.emnlp-main.44/
DOI:
Bibkey:
Cite (ACL):
Qile Wan, Davide Venditti, Fabio Massimo Zanzotto, Iryna Gurevych, and Lizhen Qu. 2026. Retrieving Facts or Reinforcing Beliefs? Towards Understanding Confirmation Bias in RAG Systems for Scientific Claim Verification. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 958–974, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Retrieving Facts or Reinforcing Beliefs? Towards Understanding Confirmation Bias in RAG Systems for Scientific Claim Verification (Wan et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.44.pdf