The three repetitions are regularized with certain conditions, such as the frequency distribution of the named entity types in a named entity recognition (NER) task, to reduce the unintentional introduced difference in the frequency distributions between the training and validation sets due to the random partitioning of a corpus and to make the comparison more reliable.
the m × 2 BCV estimator of certain evaluation metrics pos-sesses a minimum variance, which ensures that the tests on the 3 × 2 BCV have higher powers and replicabilities (Wang et al., 2014(Wang et al., , 2017b.