Don’t Use English Dev: On the Zero-Shot Cross-Lingual Evaluation of Contextual Embeddings

Phillip Keung, Yichao Lu, Julian Salazar, Vikas Bhardwaj


Abstract
Multilingual contextual embeddings have demonstrated state-of-the-art performance in zero-shot cross-lingual transfer learning, where multilingual BERT is fine-tuned on one source language and evaluated on a different target language. However, published results for mBERT zero-shot accuracy vary as much as 17 points on the MLDoc classification task across four papers. We show that the standard practice of using English dev accuracy for model selection in the zero-shot setting makes it difficult to obtain reproducible results on the MLDoc and XNLI tasks. English dev accuracy is often uncorrelated (or even anti-correlated) with target language accuracy, and zero-shot performance varies greatly at different points in the same fine-tuning run and between different fine-tuning runs. These reproducibility issues are also present for other tasks with different pre-trained embeddings (e.g., MLQA with XLM-R). We recommend providing oracle scores alongside zero-shot results: still fine-tune using English data, but choose a checkpoint with the target dev set. Reporting this upper bound makes results more consistent by avoiding arbitrarily bad checkpoints.
Anthology ID:
2020.emnlp-main.40
Volume:
Proceedings of the 2020 Conference on Empirical Methods in Natural Language Processing (EMNLP)
Month:
November
Year:
2020
Address:
Online
Venue:
EMNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
549–554
Language:
URL:
https://aclanthology.org/2020.emnlp-main.40
DOI:
10.18653/v1/2020.emnlp-main.40
Bibkey:
Cite (ACL):
Phillip Keung, Yichao Lu, Julian Salazar, and Vikas Bhardwaj. 2020. Don’t Use English Dev: On the Zero-Shot Cross-Lingual Evaluation of Contextual Embeddings. In Proceedings of the 2020 Conference on Empirical Methods in Natural Language Processing (EMNLP), pages 549–554, Online. Association for Computational Linguistics.
Cite (Informal):
Don’t Use English Dev: On the Zero-Shot Cross-Lingual Evaluation of Contextual Embeddings (Keung et al., EMNLP 2020)
Copy Citation:
PDF:
https://aclanthology.org/2020.emnlp-main.40.pdf
Video:
 https://slideslive.com/38938787
Data
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