Through our experiments, we found that P(H i |w i-2 w i-1 ) is a poor estimator of category probability; in fact, the unigram estimate P(H i ) achieved better results in our experiments as shown in Section 6.1.
we also used the unigram estimate for word category probability in our 3 Since the POS-tagger does not identify phrases, our implementation does not identify precisely one headword for a phrase, but identify multiple headwords in the case of compounds.