On 3 May 2011 20:50, peter dalgaard <pda...@gmail.com> wrote:
>
> On Apr 28, 2011, at 15:18 , JP wrote:
>
>>
>>
>> I have found that when doing a wilcoxon signed ranked test you should report:
>>
>> - The median value (and not the mean or sd, presumably because of the
>> underlying potential non normal distribution)
>> - The Z score (or value)
>> - r
>> - p value
>>
>
> ...printed on 40g/m^2 acid free paper with a pencil of 3B softness?
>
> Seriously, with nonparametrics, the p value is the only thing of real
> interest, the other stuff is just attempting to check on authors doing their
> calculations properly. The median difference is of some interest, but it is
> not actually what is being tested, and in heavily tied data, it could even be
> zero with a highly significant p-value. The Z score can in principle be
> extracted from the p value (qnorm(p/2), basically) but it's obviously
> unstable in the extreme cases. What is r? The correlation? Pearson, not
> Spearman?
>
Thanks for this Peter - a couple of more questions:
a <- rnorm(500)
b <- runif(500, min=0, max=1)
x <- wilcox.test(a, b, alternative="two.sided", exact=T, paired=T)
x$statistic
V
31835
What is V? (is that the value Z of the test statistic)?
z.score <- qnorm(x$p.value/2)
[1] -9.805352
But what does this zscore show in practice?
The d.f. are suggested to be reported here:
http://staff.bath.ac.uk/pssiw/stats2/page2/page3/page3.html
And r is mentioned here
http://huberb.people.cofc.edu/Guide/Reporting_Statistics%20in%20Psychology.pdfs
>> My questions are:
>>
>> - Are the above enough/correct values to report (some places even
>> quote W and df) ?
>
> df is silly, and/or blatantly wrong...
>
>> What else would you suggest?
>> - How do I calculate the Z score and r for the above example?
>> - How do I get each statistic from the pairwise.wilcox.test call?
>>
>> Many Thanks
>> JP
>>
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>
> --
> Peter Dalgaard
> Center for Statistics, Copenhagen Business School
> Solbjerg Plads 3, 2000 Frederiksberg, Denmark
> Phone: (+45)38153501
> Email: pd....@cbs.dk Priv: pda...@gmail.com
>
>
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