Rejection is deciding whether the recognition is correct.
Confidence is the probability that the recognition is correct.
This thesis presents new methods of rejecting errors and estimating confidence for telephone speech. These are also called word or utterance verification and can be used in wordspotting or voice-response systems. Language models are not considered. In vocabulary-dependent rejection all words in the target vocabulary are known in advance and a strategy can be developed for confirming each word. The majority of the thesis concerns vocabulary-independent confidence and rejection based on phonetic word models.