Overfitting Mitigation via Singular Value Decomposition in Minimum Bayes Risk Decoding

Riza Setiawan Soetedjo, Yusuke Sakai, Hidetaka Kamigaito, Katsuhiko Hayashi, Taro Watanabe


Abstract
Minimum Bayes Risk (MBR) decoding enables high-quality text generation by selecting the hypothesis that maximizes a utility metric over sampled pseudo-references. However, it is highly susceptible to metric overfitting: it can irregularly inflate the chosen utility metric at the direct expense of other unoptimized evaluation metrics. To mitigate this, we introduce SVD-MBR, which frames the pairwise utility matrix as a noisy information signal. By computing a low-rank approximation via Singular Value Decomposition (SVD) and retaining only the top-k components, we effectively decouple true consensus from metric noise. Experiments demonstrate that SVD-MBR successfully regularizes decoding, yielding substantial gains across a range of generalized metrics. Furthermore, we reveal that this denoising is metric-dependent: neural metrics encode a robust low-rank consensus ideal for SVD, whereas surface-level metrics struggle to separate signal from metric noise.
Anthology ID:
2026.emnlp-main.2570
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:
58374–58401
Language:
URL:
https://aclanthology.org/2026.emnlp-main.2570/
DOI:
Bibkey:
Cite (ACL):
Riza Setiawan Soetedjo, Yusuke Sakai, Hidetaka Kamigaito, Katsuhiko Hayashi, and Taro Watanabe. 2026. Overfitting Mitigation via Singular Value Decomposition in Minimum Bayes Risk Decoding. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 58374–58401, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Overfitting Mitigation via Singular Value Decomposition in Minimum Bayes Risk Decoding (Soetedjo et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.2570.pdf