From: Greg Snow <Greg.Snow_at_imail.org>

Date: Fri, 25 Jun 2010 12:55:38 -0600

Date: Fri, 25 Jun 2010 12:55:38 -0600

Let me see if I understand. You actually have the data for the whole population (the entire piece) but you have some pre-defined sections that you want to see if they differ from the population, or more meaningfully they are different from a randomly selected set of measures. Is that correct?

-- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.snow_at_imail.org 801.408.8111Received on Fri 25 Jun 2010 - 18:58:07 GMT

> -----Original Message-----

> From: r-help-bounces_at_r-project.org [mailto:r-help-bounces_at_r-> project.org] On Behalf Of Atte Tenkanen> Sent: Thursday, June 24, 2010 11:04 PM> To: David Winsemius> Cc: R mailing list> Subject: Re: [R] Wilcoxon signed rank test and its requirements>> The values come from this kind of process:> The musical composition is segmented into so-called 'pitch-class> segments' and these segments are compared with one reference set with a> distance function. Only some distance values are possible. These> distance values can be averaged over music bars which produces smoother> distribution and the 'comparison curve' that illustrates the distances> according to the reference set through a musical piece result in more> readable curve (see e.g. http://users.utu.fi/attenka/with6.jpg ), but I> would prefer to use original values.>> then, I want to pick only some regions from the piece and compare those> values of those regions, whether they are higher than the mean of all> values.>> 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_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.

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