calculating confidence while doing classification

Question

I am using a Naive Bayes algorithm to predict movie ratings as positive or negative. I have been able to rate movies with 81% accuracy. I am, however, trying to assign a 'confidence level' for each of the ratings as well.

I am trying to identify how I can tell the user something like "we think that the review is positive with 80% confidence". Can someone help me understand how I can calculate a confidence level to our classification result?

Answer 1

You can report the probability P(y|x) that Naive Bayes calculates. (But note that Naive Bayes isn't a very good probability model, even if it's not too bad a classifier.)