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

[Uwe Ligges]

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",
> p.adj="bonferroni", exact=F, paired=T)
>
> 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
>
> ______________________________________________
> 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.