[R] Mann-Whitney & Wilcoxon Rank Sum

From: Jim BRINDLE <j_brindle_at_hotmail.com>
Date: Mon 16 May 2005 - 14:37:40 EST


Hello,

I am hoping someone could shed some light into the Wilcoxon Rank Sum Test for me? In looking through Stats references, the Mann-Whitney U-test and the Wilcoxon Rank Sum Test are statistically equivalent. When using the following dataset:

m <- c(2.0863,2.1340,2.1008,1.9565,2.0413,NA,NA) f <- c(1.8938,1.9709,1.8613,2.0836,1.9485,2.0630,1.9143)

and the wilcox.test command as below:

wilcox.test(m,f, paired = FALSE, alternative = c("two.sided"))

I get a test statistic (W) of 30. When I perform this test by hand utilizing the methodology laid out in Ch. 6 of Ott & Longnecker I get a value of 45. Any insight or good reference(s) as to the algorithm R is using or this issue in general would be most appreciated.

Thanks....



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