Re: [R] Wilcoxon signed rank test and its requirements

From: Joris Meys <jorismeys_at_gmail.com>
Date: Wed, 23 Jun 2010 23:51:19 +0200

On Wed, Jun 23, 2010 at 10:27 PM, Atte Tenkanen <attenka_at_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.Meys_at_Ugent.be
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Received on Wed 23 Jun 2010 - 21:54:04 GMT

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