1. A method of automatic speech recognition, comprising the steps of: (a) receiving an utterance from a user via a microphone that converts the utterance into a speech signal; (b) pre-processing the speech signal using a processor to extract acoustic data from the received speech signal; (c) identifying at least one user-specific characteristic in response to the extracted acoustic data; and (d) determining a user-specific confidence threshold responsive to the at least one user-specific characteristic.