[R] Mann-Whitney & Wilcoxon Rank Sum

Jim BRINDLE j_brindle at hotmail.com
Mon May 16 06:37:40 CEST 2005


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.


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