POS tagging is used as the first step in many NLP workflows, although the accuracy of tag assignment frequently goes unchecked. We hypothesize that changing the training corpora for a parser will affect its POS tagging of a target corpus. To this end we train the Charniak-Lease parser on the WSJ corpus and two biomedical corpora and evaluate its output to MedPost, a POS tagger with a reported 97% accuracy on biomedical text. Our findings indicate that using biomedical training corpora significantly improves performance, but that minor differences in the biomedical training corpora have a significant effect on the correctness of POS tagging. Specifically, the tagging of hyphenated words and verbs was affected. This work suggests that the choice of training corpora is crucial to domain targeted NLP analysis
