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In this paper, we document our efforts to extend our statistical question answering system for TREC-11. We incorporated a web search feature, and novel extensions of statistical machine translation as well as extracting lexical patterns for exact answers from a supervised corpus. Without modification to our base set of thirty-one categories, we were able to achieve a confidence weighted score of 0.455 and an accuracy of 29%. We improved our model on selecting exact answers by insisting on exact answers in the training corpus and this resulted in a 7% gain on TREC-11 but a much larger gain of 46% on TREC-10.
Ittycheriah et al. (Sun,) studied this question.