So I checked it with the wilcox_test in the coin library, and got the same result. That makes me more confident that I made a mistake, but still doesn't help me find it
d = data.frame(value=c(dropouts,remain),group=c(rep("dropout",length(dropouts)),rep("remain",length(remain)))) wilcox_test(value~group,data=d) Sam On Thu, Oct 6, 2011 at 10:35 AM, Sam Stewart <rhelp.st...@gmail.com> wrote: > Hello List, > > I'm trying to prepare some lecture notes on non parametric methods, > and I can't manually reproduce the results of the wilcox.test function > for ordinal data. > > The data I'm using are from David Howell's website, available here > > http://www.uvm.edu/~dhowell/StatPages/More_Stuff/OrdinalChisq/OrdinalChiSq.html > > If I run the wilcox.test function on the data I get a p-value of > .0407, but when I do it myself I get a p-value of 0.0530. It's not so > much the jump across 0.05, but the fact that I thought I knew what the > function was doing. > > I know from the R help page that there is some controversy about how > exactly to calculate the test statistic, but that's not what is > causing the problem, as I can get the same W value. Am I calculating > the test statistic incorrectly? > > Thanks, sample code below > Sam Stewart > > #Ordinal example > dropouts = c(rep(0,25),rep(3,10),rep(2,9),rep(1,13),rep(4,6)) > remain = c(rep(0,31),rep(3,2),rep(2,6),rep(1,21),rep(4,3)) > tab2 = rbind(table(dropouts),table(remain)) > ordTest = wilcox.test(x=dropouts,y=remain,correct=FALSE,exact=FALSE) > cumsum(colSums(tab2)) > W = > max(c(sum(rank(cbind(dropouts,remain))[1:length(dropouts)]),sum(rank(cbind(dropouts,remain))[-(1:length(dropouts))]))) > n1 = length(dropouts) > n2 = length(remain) > testStat = (S-n1*(n1+n2+1)/2)/(sqrt(n1*n2*(n1+n2+1)/12)) > 2*(1-pnorm(testStat)) > ______________________________________________ R-help@r-project.org 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.