Is Human Annotation Necessary? Iterative MBR Distillation for Error Span Detection in Machine Translation

Boxuan Lyu, Haiyue Song, Zhi Qu


Abstract
Error Span Detection (ESD) is a crucial subtask in Machine Translation (MT) evaluation, aiming to identify the location and severity of translation errors. While fine-tuning models on human-annotated data improves ESD performance, acquiring such data is expensive and prone to inconsistencies among annotators. To address this, we propose a novel self-evolution framework based on Minimum Bayes Risk (MBR) decoding, named Iterative MBR Distillation for ESD, which eliminates the reliance on human annotations by leveraging an off-the-shelf LLM to generate pseudo-labels. Extensive experiments on the WMT Metrics Shared Task datasets demonstrate that models trained solely on these self-generated pseudo-labels outperform both unadapted base model and supervised baselines trained on human annotations at the system and span levels, while maintaining competitive sentence-level performance.
Anthology ID:
2026.findings-emnlp.169
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
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
3567–3577
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.169/
DOI:
Bibkey:
Cite (ACL):
Boxuan Lyu, Haiyue Song, and Zhi Qu. 2026. Is Human Annotation Necessary? Iterative MBR Distillation for Error Span Detection in Machine Translation. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 3567–3577, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Is Human Annotation Necessary? Iterative MBR Distillation for Error Span Detection in Machine Translation (Lyu et al., Findings 2026)
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https://aclanthology.org/2026.findings-emnlp.169.pdf