The other approach, and the focus of this paper, is co-training (Sarkar, 2001), a mostlyunsupervised algorithm that replaces the human by having two (or more) parsers label training examples for each other.
because the labeled sentences selected by S diff-10% contain more mistakes than those selected by S above-90% , S diff-10% requires slightly more corrections than S above-90% for the same level of parsing performance; though both require fewer corrections than the reference case of no selection (Figure 4(b)).