(2010) drew (R, t) pairs from each of five frequency bands in the entire British National Corpus (BNC): 50-100 occurrences; 101-200; 201-500; 500-1000; and more than 1000.
we use only half of BNC as our test corpus, so to obtain a comparable test set, we drew 20 (R, t) pairs from each of the corresponding frequency bands in that half: 26-50 occurrences; 51-100; 101-250; 251-500; and more than 500.