Tables of Critical Values for the Pratt Matched Pair Signed Rank Statistic

In the nonparametric comparison of two treatments using paired data, one frequently obtains zeros when computing the absolute difference for each of the N pairs. While Wilcoxon recommends omitting the zeros, Pratt argues that all N differences should be ranked and that only the ranks associated with the nonzero differences (n) be used in the test. Tables of critical values of the Pratt signed rank statistic are presented for n = 5(1) 50 nonzero differences and Z = 0(1) 20 difference-scores of zero at two-tail probability levels of .10, .05, .02, and .01.