Before revision:  Among them, we found that using the prior distribution of answer positions as a bias model is very effective at reducing position bias  recovering the performance of BERT from 35.24\% to 81.17 \% when trained on a biased SQuAD dataset.
After revision:  Among them, we found that using the prior distribution of answer positions as a bias model is very effective at reducing position bias recovering the performance of BERT from 37.48\% to 81.64 \% when trained on a biased SQuAD dataset.