Beyond Consensus: Diagnosing Coverage, Majority Bias, and Grounding Equity in High-Stakes Multi-Document Diversity Summarization

Jane Arleth dela Cruz, Iris Hendrickx, Martha Larson


Abstract
Multi-document diversity summarization (MDDS) in high-stakes domains such as crisis response demands fundamentally different capabilities than consensus-based summarization. While standard summarization focus on fluency and faithfulness, high-stakes tasks would also require: maximizing coverage of divergent information, identifying unique information clusters, and providing verifiable citations to source documents. Existing evaluation frameworks fail to capture these task-specific requirements. Our study introduces a comprehensive evaluation framework for high-stakes MDDS, validated on a multi-source crisis dataset that we developed covering ten crisis events. We propose novel metrics, Comprehensive Coverage Score, Frequency-Salience Correlation, and Citation-Frequency Correlation, to diagnose critical failure modes in six off-the-shelf large language models (LLMs). Our results allow us to identify three critical failure modes of LLMs: (1) a consensus trap in coverage: where models capture high-level information clusters, but miss specific, actionable details needed for decision-making; (2) majority bias, where more frequent information are prioritized over rare but important ones and; (3) a verifiability gap, where citations of rare claims are less reliable
Anthology ID:
2026.findings-aacl.246
Volume:
Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026
Month:
November
Year:
2026
Address:
Hengqin, China
Editors:
Yue Zhang, Ruifeng Xu, Ayu Purwarianti, Tong Rong, Jun Suzuki
Venue:
Findings
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
4831–4845
Language:
URL:
https://aclanthology.org/2026.findings-aacl.246/
DOI:
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Cite (ACL):
Jane Arleth dela Cruz, Iris Hendrickx, and Martha Larson. 2026. Beyond Consensus: Diagnosing Coverage, Majority Bias, and Grounding Equity in High-Stakes Multi-Document Diversity Summarization. In Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026, pages 4831–4845, Hengqin, China. Association for Computational Linguistics.
Cite (Informal):
Beyond Consensus: Diagnosing Coverage, Majority Bias, and Grounding Equity in High-Stakes Multi-Document Diversity Summarization (dela Cruz et al., Findings 2026)
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https://aclanthology.org/2026.findings-aacl.246.pdf