Also, as far as I know just for historical consistency, the test statistic in R is the rank sum of the first group MINUS its minimum possible value: W = 110.5 - sum(1:13) = 19.5
-pd > On 21 Apr 2017, at 14:54 , Achim Zeileis <achim.zeil...@uibk.ac.at> wrote: > > On Fri, 21 Apr 2017, Tripoli Massimiliano wrote: > >> Dear R users, >> Why the result of Wilcoxon sum rank test by R is different from sas >> >> https://support.sas.com/documentation/cdl/en/statug/63033/HTML/default/viewer.htm#statug_npar1way_sect022.htm >> >> The code is next: >> >> sampleA <- c(1.94, 1.94, 2.92, 2.92, 2.92, 2.92, 3.27, 3.27, 3.27, 3.27, >> 3.7, 3.7, 3.74) >> >> sampleB <- c(3.27, 3.27, 3.27, 3.7, 3.7, 3.74) >> wilcox.test(A,B,paired = F) > > There are different ways how to compute or approximate the asymptotic or > exact conditional distribution of the test statistic: > > SAS reports an asymptotic normal approximation (apparently without continuity > correction along with an asymptotic t approximation and the exact conditional > distribution. > > Base R's stats::wilcox.test can either report the exact conditional > distribution (but only if there are no ties) or the asymptotic normal > distribution (with or without continuity correction). In small samples the > default is to use the former but a warning is issued when there are ties (as > in your case). > > Furthermore, coin::wilcox_test can report either the asymptotic normal > distribution (without continuity correction) or the exact conditional > distribution (even in the presence of ties). > > Thus: > > ## collect data in data.frame > d <- data.frame( > y = c(sampleA, sampleB), > x = factor(rep(0:1, c(length(sampleA), length(sampleB)))) > ) > > ## asymptotic normal distribution without continuity correction > ## (p = 0.0764) > stats::wilcox.test(y ~ x, data = d, exact = FALSE, correct = FALSE) > coin::wilcox_test(y ~ x, data = d, distribution = "asymptotic") > > ## exact conditional distribution (p = 0.1054) > coin::wilcox_test(y ~ x, data = d, distribution = "exact") > > These match SAS's results. The default result of stats::wilcox.test is > different as explained by the warning issued. > > hth, > Z > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Office: A 4.23 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
