18. An engine according to claim 16 , wherein the confidence score threshold is a reject threshold such that speech recognition results having a confidence score above the reject threshold require user confirmation and speech recognition results having a confidence score below the reject threshold are rejected as incorrect without user confirmation.
16. A speech recognition engine implemented as a plurality of computer processes functioning in a computer processor employing at least one hardware implemented computer processor and characterized by an associated receiver operating characteristic (ROC) curve, the engine comprising: a results confirmation process that interprets user confirmation of speech recognition results within a given confidence score threshold to create a confirmed portion of the ROC curve for the speech recognition engine; a curve extension process that extends the confirmed portion of the ROC curve by extrapolation of unconfirmed speech recognition results beyond the confidence score threshold to generate an extended ROC curve; and a threshold adjustment process that adjusts the confidence score threshold based on the extended ROC curve to meet target operating constraints for operating the speech recognition engine to perform automatic speech recognition of user speech inputs.