# Re: [R] Simple General Statistics and R question (with 3 line example) - get z value from pairwise.wilcox.test

From: Uwe Ligges <ligges_at_statistik.tu-dortmund.de>
Date: Mon, 02 May 2011 10:16:04 +0200

To get the statsitics, you will have to run each wilcox.test manually. the pairwise... version just extracts the p-values and adjusts them.

Uwe Ligges

On 28.04.2011 15:18, JP wrote:
> Hi there,
>
> I am trying to do multiple pairwise Wilcoxon signed rank tests in a
> manner similar to:
>
> a<- c(runif(1000, min=1,max=50), rnorm(1000, 50), rnorm(1000, 49.9,
> 0.5), rgeom(1000, 0.5))
> b<- c(rep("group_a", 1000), rep("group_b", 1000), rep("group_c",
> 1000), rep("group_d", 1000))
> pairwise.wilcox.test(a, b, alternative="two.sided",
>
> This gives me the following output:
>
> group_a group_b group_c
> group_b<2e-16 - -
> group_c<2e-16 0.25 -
> group_d<2e-16<2e-16<2e-16
>
> (which is kind of expected since group_b and group_c have similar distributions)
>
> 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
>
> My questions are:
>
> - Are the above enough/correct values to report (some places even
> quote W and df) ? 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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