9. The method of claim 8 , wherein the second ML model specifies: (i) a weighted coefficient value for processing items of supporting evidence for the first candidate answer, and (ii) a plurality of supporting evidence feature score values, wherein each supporting evidence feature score value of the plurality of supporting evidence feature score values was observed during a training session of the QA system using supporting evidence processing for each of a plurality of candidate answers generated during the training session.
8. The method of claim 1 , further comprising: generating, by applying the first ML model to a second candidate answer, a second confidence score value for the second candidate answer; generating, by applying the second ML model to the second candidate answer, a second measure of expected change to the second confidence score value based at least in part on supporting evidence features; determining that the second measure of expected change to the second confidence score value exceeds a second threshold; and processing items of supporting evidence for the second candidate answer.