MetricX-23: The Google Submission to the WMT 2023 Metrics Shared Task
Written for the Research library (claude-opus-5-5) from the paper text. Original — aclanthology.org/2023.wmt-1.63.pdf
Summary
The paper describes Google's MetricX-23 entries to the WMT 2023 Metrics Shared Task. The goal is an automatic MT evaluation metric that agrees closely with human quality judgments. MetricX-23 is a learned regression metric. It reads the candidate translation joined with the reference (or with the source, for the reference-free QE variant) and outputs a single quality score.
Three systems were submitted, each in a reference-based and a QE version. Two are built on mT5-XXL and one on PaLM 2 (Bison). They differ in the training data and in the pretrained backbone. The authors used mT5-XL to run ablations on:
- which human-rating data to use,
- how to normalize labels,
- how much synthetic data to add,
- model size,
- choice of backbone.
The strongest recipe fine-tunes in two stages, first on DA ratings and then on MQM ratings, and mixes in synthetic examples. Larger backbones clearly help. One recurring finding is that improving segment-level and system-level correlation at the same time is hard, because gains on one level often cost the other. The mT5-based checkpoints and code are publicly released, which gives practitioners a strong, reusable MT metric.
Key points
- Submissions:
- MetricX-23 (primary) is mT5-XXL (13B) fine-tuned on z-normalized, clipped DA data from 2015–2020, then on raw MQM scores from 2020–2021 plus synthetic data.
- The "-b" variant also adds MQM 2022.
- The "-c" variant replaces mT5 with PaLM 2 Bison.
- Main ablation findings:
- Z-normalizing DA scores trades segment-level performance against system-level performance.
- Raw MQM labels work better than normalized ones.
- Training on DA followed by MQM beats training on either alone.
- Synthetic data is needed so the metric scores a reference against itself above an MT output.
- Evaluation: MQM 2022 was the main meta-evaluation set, plus the DEMETR challenge set. The measures were system-level Pearson's r and pairwise accuracy, and segment-level Pearson's r and group-by-item pairwise accuracy with tie calibration.
- Training data: over 2M raw DA ratings (about 1M after aggregation) across 40 language pairs. Training ran on TensorFlow/T5X with 64 TPUs, using Adafactor and an MSE loss.
- Release: mT5-based models are published as PyTorch checkpoints at github.com/google-research/metricx.
Cited by
- Results of WMT23 Metrics Shared Task: Metrics Might Be Guilty but References Are Not Innocent
- xCOMET: Transparent Machine Translation Evaluation through Fine-grained Error Detection
- MetricX-24: The Google Submission to the WMT 2024 Metrics Shared Task
- Findings of the WMT24 General Machine Translation Shared Task: The LLM Era Is Here but MT Is Not Solved Yet
- Beyond Correlation: Interpretable Evaluation of Machine Translation Metrics
Cite
@inproceedings{juraska2023metricx,
title = {{MetricX-23: The Google Submission to the WMT 2023 Metrics Shared Task}},
author = {Juraska, Juraj and Finkelstein, Mara and Deutsch, Daniel and Siddhant, Aditya and Mirzazadeh, Mehdi and Freitag, Markus},
booktitle = {Proceedings of the Eighth Conference on Machine Translation},
year = {2023},
doi = {10.18653/v1/2023.wmt-1.63},
url = {https://doi.org/10.18653/v1/2023.wmt-1.63}
}References
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