Hi folks, sorry for this beginner question but what means a p-value = NA on a menn-whitney test? v1 <- c(0.022, 0.022, 0.022, 0.022, 0.022, 0.022) v2 <- c(0.022, 0.022, 0.022, 0.022, 0.022) wilcox.test(v1, v2, PAIRED=FALSE) W = 15, p-value = NA I know that there's no statistical difference between v1 and v2, so why my p-value is not ONE ?? Can I consider p-value= NA as ONE ?? what i do when get this type of value on wilcox.test ??? PS: sorry for my bad english. [[alternative HTML version deleted]]
Hi Ambar, v1 and v2 are constants. they need to be variables. try e.g., v1 <- c(0.021, 0.022, 0.022, 0.022, 0.022, 0.022) v2 <- c(0.021, 0.022, 0.022, 0.022, 0.022) wilcox.test(v1, v2, PAIRED=FALSE) -Ista On Thu, Nov 5, 2009 at 7:23 PM, Ambar Amarelo <ambar.amarelo at gmail.com> wrote:> Hi folks, sorry for this beginner question but what means a p-value = NA on > a menn-whitney test? > > v1 <- c(0.022, 0.022, 0.022, 0.022, 0.022, 0.022) > v2 <- c(0.022, 0.022, 0.022, 0.022, 0.022) > wilcox.test(v1, v2, PAIRED=FALSE) > > W = 15, p-value = NA > > I know that there's no statistical difference between v1 and v2, so why my > p-value is not ONE ?? > > Can I consider p-value= NA ?as ONE ?? > what i do when get this type of value on wilcox.test ??? > > > PS: sorry for my bad english. > > ? ? ? ?[[alternative HTML version deleted]] > > ______________________________________________ > R-help at 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. >-- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org
Ambar Amarelo wrote:> Hi folks, sorry for this beginner question but what means a p-value = NA on > a menn-whitney test? > > v1 <- c(0.022, 0.022, 0.022, 0.022, 0.022, 0.022) > v2 <- c(0.022, 0.022, 0.022, 0.022, 0.022) > wilcox.test(v1, v2, PAIRED=FALSE) > > W = 15, p-value = NA > > I know that there's no statistical difference between v1 and v2, so why my > p-value is not ONE ?? > > Can I consider p-value= NA as ONE ?? > what i do when get this type of value on wilcox.test ??? > > > PS: sorry for my bad english. > > [[alternative HTML version deleted]] >Did you read the help page? If there are ties, then a Normal approximation is used. So how would you do a Normal approximation? Try it "by hand" - you have a small enough amount of data. Try also a t.test() and see what message it gives you. BTW, there is no PAIRED argument to wilcox.test(). -- Peter Ehlers University of Calgary