Extrinsic Evaluation of Machine Translation Metrics

Nikita Moghe, Tom Sherborne, Mark Steedman, Alexandra Birch


Abstract
Automatic machine translation (MT) metrics are widely used to distinguish the quality of machine translation systems across relatively large test sets (system-level evaluation). However, it is unclear if automatic metrics are reliable at distinguishing good translations from bad translations at the sentence level (segment-level evaluation). In this paper, we investigate how useful MT metrics are at detecting the segment-level quality by correlating metrics with how useful the translations are for downstream task. We evaluate the segment-level performance of the most widely used MT metrics (chrF, COMET, BERTScore, etc.) on three downstream cross-lingual tasks (dialogue state tracking, question answering, and semantic parsing). For each task, we only have access to a monolingual task-specific model and a translation model. We calculate the correlation between the metric’s ability to predict a good/bad translation with the success/failure on the final task for the machine translated test sentences. Our experiments demonstrate that all metrics exhibit negligible correlation with the extrinsic evaluation of the downstream outcomes. We also find that the scores provided by neural metrics are not interpretable, in large part due to having undefined ranges. We synthesise our analysis into recommendations for future MT metrics to produce labels rather than scores for more informative interaction between machine translation and multilingual language understanding.
Anthology ID:
2023.acl-long.730
Volume:
Proceedings of the 61st Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
Month:
July
Year:
2023
Address:
Toronto, Canada
Editors:
Anna Rogers, Jordan Boyd-Graber, Naoaki Okazaki
Venue:
ACL
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
13060–13078
Language:
URL:
https://aclanthology.org/2023.acl-long.730
DOI:
10.18653/v1/2023.acl-long.730
Bibkey:
Cite (ACL):
Nikita Moghe, Tom Sherborne, Mark Steedman, and Alexandra Birch. 2023. Extrinsic Evaluation of Machine Translation Metrics. In Proceedings of the 61st Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers), pages 13060–13078, Toronto, Canada. Association for Computational Linguistics.
Cite (Informal):
Extrinsic Evaluation of Machine Translation Metrics (Moghe et al., ACL 2023)
Copy Citation:
PDF:
https://aclanthology.org/2023.acl-long.730.pdf
Video:
 https://aclanthology.org/2023.acl-long.730.mp4