Tagging accurately -- Don't guess if you know
  We discuss combining knowledge-based (or rule-based) and statistical part-of-speech taggers. We use two mature taggers, ENGCG and Xerox Tagger, to independently tag the same text and combine the results to produce a fully disambiguated text. In a 27000 word test sample taken from a previously unseen corpus we achieve 98.5% accuracy. This paper presents the data in detail. We describe the problems we encountered in the course of combining the two taggers and discuss the problem of evaluating taggers. 
Pasi Tapanainen (Rank Xerox Research Centre, Grenoble Laboratory),   Atro Voutilainen (Research Unit for Computational Lingu...