Before revision:  We also explore using our model conditioned on the source instead of the reference, and find that it outperforms every quality estimation as a metric system from the WMT19 shared task on quality estimation by a statistically significant margin in every language pair.
After revision:  We also explore using our model conditioned on the source instead of the reference, and find that it significantly outperforms every submission to the WMT 2019 shared task on quality estimation by a statistically significant margin in every language pair.