Comparing Corpora

Corpus linguistics lacks strategies for describing and comparing corpora. Currently most descriptions of corpora are textual, and questions such as ‘what sort of a corpus is this? ’, or ‘how does this corpus compare to that? ’ can only be answered impressionistically. This paper considers various ways in which different corpora can be compared more objectively. First we address the issue, ‘which words are particularly characteristic of a corpus? ’, reviewing and critiquing the statistical methods which have been applied to the question and proposing the use of the Mann-Whitney ranks test. Results of two corpus comparisons using the ranks test are presented. Then, we consider measures for corpus similarity. After discussing limitations of the idea of corpus similarity, we present a method for evaluating corpus similarity measures. We consider several measures and establish that a2-based one performs best. All methods considered in this paper are based on word and ngram frequencies; the strategy is defended.