The PPCEME was constructed from the Helsinki Corpus samples of the appropriate
period. Wherever possible sample texts or text types were extended so that each genre
was, for each time period, represented by a sample of approximately 50,000 words. This
extension improves the usefulness of the corpora for syntactic research, since in that
domain, the utility of a corpus depends on the number of clauses rather than the number
of words that it contains.