1. A speaker verification method comprising: performing operations executed by a speaker verification machine, the operations comprising: comparing a plurality of different test utterances to a plurality of training utterances for a speaker to form a plurality of preliminary verification decisions, one preliminary verification decision for each of the plurality of different test utterances; weighting each of the plurality of preliminary verification decisions based on a historical error rate corresponding to a respective one of the test utterances; and combining the weighted preliminary verification decisions to form a verification decision.