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Re: st: Nemenyi test
From
Célia Dechavanne <[email protected]>
To
[email protected]
Subject
Re: st: Nemenyi test
Date
Thu, 29 Aug 2013 08:22:19 +0200
Thank you for your help.
My first mail was not enough clear, sorry for that. The five groups are
small (minimum n=11 and maximum n=26). The KW test gives a significant
difference between the groups, now I would like to compare 2 by 2. But I
can't perform pairwise comparison, I would like to compare the shift
between the five groups. I hope is better clear now.
Thank you so much for the time spent to answer.
Best
Celia
Le mercredi 28 août 18:29, Marta García-Granero a écrit :
I have Hochberg&Tamhane "Multiple Comparisons Procedures", and there
are a couple of references for a Nemenyi procedure, one for pairwise
signed ranks tests (after a non-parametric K related samples omnibus
test) and another for pairwise median tests, after a k-samples median
test (not Kruskal-Wallis). This last method is also known as Levy test.
Unless there is another "Nemenyi procedure" not mentioned in H&T book,
I think Celia is a bit confused, since she has performed a
Kruskal-Wallis test, not a k-medians test. Anyway, I have found a web
page that described multiple comparisons method named Nemenyi after a
KW test...
Maybe the simplest pairwise comparison method she can use is pairwise
rank-sums (AKA: Mann-Whitney's U tests) with Sidak adjustment.
This program is rather unpolished (absolutely no error trapping or
handling), but it does the task (quick&dirty solution):
program multimw,nclass
version 12
args x y
confirm var `x'
confirm var `y'
sum `y',meanonly
local comp=r(max)*(r(max)-1)/2
qui levelsof `y',local(levels)
foreach i of local levels{
foreach j of local levels{
if `i'<`j'{
quietly ranksum `x' if (`y'==`i')|(`y'==`j'), by(`y')
display `j' _c
display " vs " `i' _c
display "p = " %6.4f 2*(1-normal(`r(z)')) " " _c
display "p’= " %6.4f 1-(1-2*(1-normal(`r(z)')))^comp
}
}
}
end
It gives both unadjusted and adjusted p-values.
HTH.
Marta GG
El 27/08/2013 13:22, David Hoaglin escribió:
Celia,
I'm not sure what you mean by the "Nemenyi test." Kruskal-Wallis and
similar tests based on ranks do not compare distributions. They focus
on shifts (e.g., differences in medians among distributions that have
the same shape).
How do your continuous distributions behave? What is the reason for
comparing the whole distributions? How large are the samples?
David Hoaglin
On Tue, Aug 27, 2013 at 2:16 AM, Célia Dechavanne <[email protected]>
wrote:
I am attempting to compare the distributions of a continuous variable
between five groups after a Kruskal Wallis in Stata without success.
I think that Nemenyi test is the one I need, but I don't find
anything in
Stata. Could you help me to perform this test?
Thanks for your help,
--
Célia Dechavanne
INSERM - UMR S665
Equipe 3 - Pathogénèse du paludisme sévère
6, rue Alexandre Cabanel
75739 Paris Cedex 15
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