LO 7.2.2.A

Learning Objective: Explain why the denominator can be dropped from Bayes Rule in the context of classifying a document.

Review:

• Why the denominator can be dropped.

Naive Bayes is a probabilistic classifier that returns class , which has the maximum posterior probability given a document d

When we apply the above max posterior probability formula to all classes  c ∈ C, we note that the ranking of the class posterior probabilities is not affected by the presence of the denominator term (as it is the same for all classes). To speed up the calculations, we can therefore remove the denominator term from the formula and then express it as