Thus, if w 1 w 2 w 3 w 4 w 5 was not observed in the training corpus, p(w In most smoothing methods, the lower-order models, for all N > 1, are recursively estimated in the same way as the highest-order model.
the smoothing method of Kneser and Ney (1995) and its variants are the most effective methods known (Chen and Goodman, 1998), and they use a different way of computing N-gram counts for all the lower-order models used for smoothing.