Xiao and McEnery (2005:70) compared two reference corpora, the 100-million-word British National Corpus and the one million-word Freiburg-LOB Corpus, and achieved almost identical key word lists, thus concluding that the size of the reference corpus is not very important in making a key word list.
the results become a lot poorer as we go further down from Line d. Tables 5 and 6 show that in both cases the reference of similar size to the target corpus gives the best, or one of the best results, especially when the reference corpus is smaller than the target.