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Re: st: RE: save p-values from Kruskal-Wallis-test


From   Nick Winter <nw53@cornell.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: save p-values from Kruskal-Wallis-test
Date   Wed, 01 Jun 2005 09:50:22 -0400

I note that the -kwallis- ado file reports a probability of 0.0001 whenever the actual chi2tail value is less than 0.0001, and to add (1e-20) to the value of the statistic before calculating the probability.

The relevant bit of code is:

max(chiprob(`Grp'[_N]-1,`K'+(1e-20)),.0001);

Presumably it never makes a substantive difference that the p-level is reported as 0.0001 when it is, in fact "less than 0.0001." But this seems odd (at best) to me, and inconsistent with Stata's style of reporting p-levels in other cases. Anyone aware of any reason for this?

--Nick Winter

--


At 04:44 AM 6/1/2005, you wrote:

return list

shows that the chi2 value and the degrees of freedon are saved in r(df) and r(chi2)

So the p-value is chi2tail(`r(df)',`r(chi2)')



-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of BBS
Querschnittsprojekt: Gerhard Schön
Sent: Wednesday, 1 June 2005 3:57 PM
To: statalist@hsphsun2.harvard.edu
Subject: st: save p-values from Kruskal-Wallis-test


Dear all,

I have to save p-values from a Kruskal-Wallis-test.
Unfortunately the command kwallis doesn't return p-
values.

. sysuse auto
. kwallis price, by(foreign)
. return list

Is there a way to obtain p-values from Kruskal-Wallis-
test in a (e)return list; maybe within other commands?

Thanks,
Gerhard

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--------------------------------------------------------
Nicholas Winter 607.255.8819 t
Assistant Professor 607.255.4530 f
Department of Government nw53@cornell.edu e
308 White Hall falcon.arts.cornell.edu/nw53 w
Cornell University
Ithaca, NY 14853-4601

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