> On Jun 23, 2010, at 9:58 PM, Atte Tenkanen wrote: > > > Thanks. What I have had to ask is that > > > > how do you test that the data is symmetric enough? > > If it is not, is it ok to use some data transformation? > > > > when it is said: > > > > "The Wilcoxon signed rank test does not assume that the data are > > sampled from a Gaussian distribution. However it does assume that > > the data are distributed symmetrically around the median. If the > > distribution is asymmetrical, the P value will not tell you much > > about whether the median is different than the hypothetical value." > > You are being misled. Simply finding a statement on a statistics > software website, even one as reputable as Graphpad (???), does not > mean that it is necessarily true. My understanding (confirmed > reviewing "Nonparametric statistical methods for complete and censored > > data" by M. M. Desu, Damaraju Raghavarao, is that the Wilcoxon signed- > > rank test does not require that the underlying distributions be > symmetric. The above quotation is highly inaccurate. > > -- > David.
Thanks. Unfortunately, I can't follow the reference at all, but I read this in that way that I can be carefree as far as the underlying distribution is concerned? Is there any other authoritative reference where that is just stated in a way "test does not require that the underlying distributions be symmetric or normal". Atte > > > >> On Wed, Jun 23, 2010 at 10:27 PM, Atte Tenkanen <atte...@utu.fi> > >> wrote: > >>> Hi all, > >>> > >>> I have a distribution, and take a sample of it. Then I compare that > >> sample with the mean of the population like here in "Wilcoxon signed > >> rank test with continuity correction": > >>> > >>>> wilcox.test(Sample,mu=mean(All), alt="two.sided") > >>> > >>> Wilcoxon signed rank test with continuity correction > >>> > >>> data: AlphaNoteOnsetDists > >>> V = 63855, p-value = 0.0002093 > >>> alternative hypothesis: true location is not equal to 0.4115136 > >>> > >>>> wilcox.test(Sample,mu=mean(All), alt = "greater") > >>> > >>> Wilcoxon signed rank test with continuity correction > >>> > >>> data: AlphaNoteOnsetDists > >>> V = 63855, p-value = 0.0001047 > >>> alternative hypothesis: true location is greater than 0.4115136 > >>> > >>> What assumptions are needed for the population? > >> > >> wikipedia says: > >> "The Wilcoxon signed-rank test is a _non-parametric_ statistical > >> hypothesis test for... " > >> it also talks about the assumptions. > >> > >>> What can we say according these results? > >>> p-value for the "less" is 0.999. > >> > >> That the p-value for less and greater seem to sum up to one, and that > >> the p-value of greater is half of that for two-sided. You shouldn't > >> ask what we can say. You should ask yourself "What was the question > >> and is this test giving me an answer on that question?" > >> > >> Cheers > >> Joris > >> > >> -- > >> Joris Meys > >> Statistical consultant > >> > >> Ghent University > >> Faculty of Bioscience Engineering > >> Department of Applied mathematics, biometrics and process control > >> > >> tel : +32 9 264 59 87 > >> joris.m...@ugent.be > >> ------------------------------- > >> Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php > > > > ______________________________________________ > > 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. > ______________________________________________ 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.
