11. A computer program product implemented in a computer readable storage medium for adjusting operation of a speech recognition engine characterized by an associated receiver operating characteristic (ROC) curve, the product comprising: program code for interpreting 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; program code for extending 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 program code for adjusting 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.
15. A product according to claim 11 , wherein the extrapolation is based on a sampling approach having user confirmation of selected speech recognition results beyond the confidence score threshold.