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that Di is continuous and that it is derived from a symmetric distribution,neither of which is normally met in IR data
...It seems therefore that some of the more sophisticated statistical tests are inappropriate
...The way it works is as follows:Let Za Q 1,Za Q 2,...P Za >Zb P Za <Zb [1]2 Under this hypothesis we expect the number of pairs which have Za >Zb to equal the number of pairs which have Za <Zb
...In IR this test is usually used as a one tailed test,that is,the alternative hypothesis prescribes the superiority of retrieval under condition a over condition b,or vice versa
...The use of the sign test raises a number of interesting points
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