On Thu, 28 Jun 2007 14:18:52 -0700 Nordlund, Dan (DSHS/RDA) wrote: > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Marcus > > Vinicius Sent: Thursday, June 28, 2007 1:32 PM > > To: [email protected] > > Subject: [R] Wilcoxon Rank Sum Test. > > > > Dear, > > > > I'm using R software to evaluate Wilcoxon Rank Sum Test and > > I' getting one > > Warning message as this: > > > > > C1dea_com > > [1] 1.000 0.345 0.200 0.208 0.508 0.480 0.545 0.563 0.451 > > 0.683 0.380 0.913 > > 1.000 0.506 > > > C1dea_sem > > [1] 1.000 0.665 0.284 0.394 0.509 0.721 0.545 0.898 0.744 > > 0.683 0.382 0.913 > > 1.000 0.970 > > > > > > > wilcox.test(C1dea_sem,C1dea_com, paired = TRUE, alternative > > = "two.sided") > > > > Wilcoxon signed rank test with continuity correction > > > > data: C1dea_sem and C1dea_com > > V = 45, p-value = 0.009152 > > alternative hypothesis: true mu is not equal to 0 > > > > Warning message: > > Cannot compute exact p-value with zeroes in: > > wilcox.test.default(C1dea_sem, > > C1dea_com, paired = TRUE, alternative = "two.sided") > > > > What is happening? > > > > Best Regards, > > > > Marcus Vinicius > > > > Marcus, > > It means that you have one or more pairs of observations (5 in your > case) where the difference is 0. The wilcox.test can only compute an > approximate p-value under these circumstances.
...while wilcox.exact() from package "exactRankTests" can evaluate the permutation distribution correctly. Z > Hope this is helpful, > > Dan > > Daniel J. Nordlund > Research and Data Analysis > Washington State Department of Social and Health Services > Olympia, WA 98504-5204 > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html and provide commented, > minimal, self-contained, reproducible code. > ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
