1. A computer-implemented method of generating personalized user models, the method comprising: receiving automatic speech recognition (ASR) output of a plurality of speech interactions with a user; receiving an ASR transcription error model characterizing how ASR transcription errors are made; generating guesses of a true transcription and a user model via an expectation maximization (EM) algorithm based on the error model and the respective ASR output; and generating a personalized user model based on the guesses.