While standard naive Bayes text classification can work well for sentiment analysis, some small changes are generally employed that improve performance. First, for sentiment classification and a number of other text classification tasks, whether a word occurs or not seems to matter more than its frequency. Thus it often improves performance to clip the word counts in each document at 1 (see the end of the chapter for pointers to these results). This variant is called binary multinomial naive Bayes or binary NB. The variant uses the same Eq. 4.10 except binary NB that for each document we remove all duplicate words before concatenating them into the single big document. Fig. 4 .3 shows an example in which a set of four documents (shortened and text-normalized for this example) are remapped to binary, with the modified counts shown in the table on the right. The example is worked without add-1 smoothing to make the differences clearer. Note that the results counts need not be 1; the word great has a count of 2 even for Binary NB, because it appears in multiple documents.