How can a trigram tagger perform worse than that of bigram?

How can a trigram tagger perform worse than that of bigram?

by Bich Ngoc Doan -
Number of replies: 0

Hi, I was revising the practical session 3 and noticed that for 3.3, the performance of the trigram tagger is worse than the ones it fallbacks on. Intuitively, it should have been better by adding another layer of n-gram, but in this case it's the opposite. What might be the reason for this to happen?

Thank you so much in advance :)