Greg Snow kirjoitti 25.6.2010 kello 21.55: > 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?
Exactly. > > If so, since you have the entire population of interest you can > create the actual sampling distribution (or a good approximation of > it). Just take random samples from the population of the given > size (matching the subset you are interested in) and calculate the > means (or other value of interest), probably 10,000 to 1,000,000 > samples. Now compare the value from your predefined subset to the > set of random values you generated to see if it is in the tail or not. Thank you! I will do this. Is this kind of !Monte Carlo -evaluation (?)" often used in statistics.If it is, do you know any reference for ti? Atte > > -- > Gregory (Greg) L. Snow Ph.D. > Statistical Data Center > Intermountain Healthcare > greg.s...@imail.org > 801.408.8111 > > >> -----Original Message----- >> From: r-help-boun...@r-project.org [mailto:r-help-boun...@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 nÅ250-300 >>>> >>> >>> 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. [[alternative HTML version deleted]]
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