As Figure 3 shows, the distribution of words to POS tags is highly skewed, with just 6 POS tags, NN, IN, NNP, DT, JJ and NNS, accounting for over 55% of the tokens in the corpus.
in the ad hoc approach the expected count plus α − 1 may be less than zero, resulting in a value of zero for the corresponding parameter (Johnson et al., 2007;.