More Evidence Is Not Always More Support: Controlled Diagnostics for Evidence Aggregation in Fact Verification

Shaoxin Zhong, Yuchen Su, Qian Liu, Michael J. Witbrock


Abstract
Final-context accuracy in multi-passage fact verification can hide whether an added passage contributes a new verdict-relevant fact or merely repeats evidence already present. We introduce a controlled same-prefix diagnostic derived from HoVer supporting-fact annotations to measure marginal evidence contribution. For each claim, a shared prefix covers one fact’s evidence while leaving another required fact absent; the next passage either repeats the covered fact or supplies the missing fact. The diagnostic contains 1,180 same-prefix pairs and an exact-repetition ladder testing whether repeated copies of one evidence sentence can change a verifier’s label. Supervised verifiers with similar clean F1 scores, from 0.6324 to 0.6528, differ sharply in eight-repeat flip rate, from 8.5% to 30.3%. Conservative pooling and natural-language-inference (NLI) scoring reduce duplicate sensitivity but give near-zero missing-fact gain, while gain-oriented systems improve gain but remain repetition-sensitive. Latent-Gated Evidence Dynamics (LGED), a compact stateful reference model, shows that low duplicate sensitivity and positive missing-fact gain can coexist. Surface controls and decision-level analyses support this diagnostic interpretation. Redundancy and reader tests extend the duplicate-sensitivity finding beyond HoVer, while prompted open-weight LLMs reveal a gap between role recognition and verdict updating.
Anthology ID:
2026.findings-emnlp.747
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
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SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
15724–15747
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URL:
https://aclanthology.org/2026.findings-emnlp.747/
DOI:
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Cite (ACL):
Shaoxin Zhong, Yuchen Su, Qian Liu, and Michael J. Witbrock. 2026. More Evidence Is Not Always More Support: Controlled Diagnostics for Evidence Aggregation in Fact Verification. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 15724–15747, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
More Evidence Is Not Always More Support: Controlled Diagnostics for Evidence Aggregation in Fact Verification (Zhong et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.747.pdf