BTW. If there is not so weak test that would be suitable for my purpose (because of the ties and the shape of the data), could I proceed this way:
It is also worth of comparing different samples taken from the data. Since the mean and sd of the data are available, could I approximate p-values using z- or t-test, just to compare several different samples? Atte > On Jun 24, 2010, at 6:58 PM, Atte Tenkanen wrote: > > > Is there anything for me? > > > > There is a lot of data, n=2418, but there are also a lot of ties. > > My sample n≈250-300 > > > > I do not understand why there should be so many ties. You have not > described the measurement process or units. ( ... although you offer a > > glipmse without much background later.) > > > i would like to test, whether the mean of the sample differ > > significantly from the population mean. > > Why? What is the purpose of this investigation? Why should the mean of > > a sample be that important? > > > > > The histogram of the population looks like in attached histogram, > > what test should I use? No choices? > > > > This distribution comes from a musical piece and the values are > > 'tonal distances'. > > > > http://users.utu.fi/attenka/Hist.png > > That picture does not offer much insidght into the features of that > measurement. It appears to have much more structure than I would > expect for a sample from a smooth unimodal underlying population. > > -- > David. > > > > > Atte > > > >> On 06/24/2010 12:40 PM, David Winsemius wrote: > >>> > >>> 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. > >>> > >> > >> To add to what David and others have said, look at the kernel that > > >> the > >> > >> U-statistic associated with the WSR test uses: the indicator (0/1) > of > >> xi > >> + xj > 0. So WSR tests H0:p=0.5 where p = the probability that the > >> average of a randomly chosen pair of values is positive. [If there > >> are > >> ties this probably needs to be worded as P[xi + xj > 0] = P[xi + xj > < > >> > >> 0], i neq j. > >> > >> Frank > >> > >> -- > >> Frank E Harrell Jr Professor and Chairman School of Medicine > >> Department of Biostatistics Vanderbilt > >> University > ______________________________________________ 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.