12. The computer readable storage medium of claim 11 , wherein calculating an initial probability θ y comprises constructing binary valued feature vectors for sentences in the training data, the binary values being 0 or 1 based on whether words are in a lexicon.
11. A computer readable storage medium including instructions readable by a computer which, when implemented, cause the computer to construct and output a statistical classifier comprising: receiving labeled training data categorized into classes; calculating an initial class probability θ y for sentences on the training data; calculating an initial probability θ ky based on probability that a word k is in class y; calculating an initial improbability θ ky based on improbability that word k is in class y; and maximizing conditional class likelihood H over the training data by iteratively recalculating the parameters θ ky , θ ky without recalculating θ y , over all classes jointly to construct the statistical classifier.