On 03.05.2011 10:33, JP wrote:
Thanks Uwe,
How do I calculate the Z score and r value - please (once I have the p values)?
Actually you calculate the p value from the statistics rathger than vice
versa. And pairwise.wilcox.test uses wilcox.test to calculate the
separate tests and adjusts the p values for multiple testing later on.
That's why I said you can manually run wilcox.test to get the separate
statistics.
Uwe Ligges
Many Thanks
JP
2011/5/2 Uwe Ligges<lig...@statistik.tu-dortmund.de>:
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
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