[R] kruskal wallis post hoc?

[peter dalgaard]

On Jan 12, 2012, at 14:11 , Frank Harrell wrote:

> The Kruskal-Wallis test is a special case of the proportional odds ordinal
> logistic model.

Eh? Can you elaborate on that?

I would expect that at best it is equivalent to some _test_ in a polr-type model. It is never really clear what the model is when some groups are different and others not.

>  You can get any contrast you want by testing regression
> coefficients.   In a couple of weeks the rms package's contrast function
> will allow for individual confidence intervals of effects that together have
> a 0.05 type I error, by using the multcomp package (called automatically
> from contrast.rms).
> Frank
> 
> Iasonas Lamprianou wrote
>> 
>> Thank you for the result, I will have a look at the link.
>> 
>>  
>> Dr. Iasonas Lamprianou
>> Department of Social and Political Sciences
>> University of Cyprus
>> 
>> 
>>> ________________________________
>>> From: Tal Galili <tal.galili@>
>>> To: Iasonas Lamprianou <lamprianou@> 
>>> Cc: "r-help@" <r-help@> 
>>> Sent: Thursday, 12 January 2012, 10:48
>>> Subject: Re: [R] kruskal wallis post hoc?
>>> 
>>> 
>>> Hi Iasonas ,
>>> This is a stat question and not an R question.
>>> But the general answer is that it could happen :)
>>> 
>>> 
>>> The R question would have been if their is a Tukey HSD for kruskel.test,
> the answer is yes:
>>> http://stats.stackexchange.com/questions/17342/is-there-a-nonparametric-equivalent-of-tukey-hsd 
>>> But if you didn't get any significant result from the pairwise comparison,
> I would say that the post hoc correction wouldn't help you (it could be that
> the reason for this significance is based on some weird contrast...)
>>> 
>>> 
>>> Best,
>>> Tal
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> ----------------Contact
> Details:-------------------------------------------------------
>>> Contact me: Tal.Galili@ |  972-52-7275845
>>> Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) |
> www.r-statistics.com (English)
>>> ----------------------------------------------------------------------------------------------
>>> 
>>> 
>>> 
>>> 
>>> 
>>> On Thu, Jan 12, 2012 at 8:35 AM, Iasonas Lamprianou <lamprianou@>
> wrote:
>>> 
>>> Dear all,
>>>> 
>>>> I run a kruskal wallis test and found significant results. Then, I
> conducted all pairwise comparisons and found no significant results. Could
> anyone please give me a hint as to why this happens or redirect me towards a
> specific web page where I can find more info? (I used alpha=5% and made no
> bonferroni or other correction for the pairwise comparisons)
>>>> Thank you
>>>> 
>>>>  
>>>> Dr. Iasonas Lamprianou
>>>> Department of Social and Political Sciences
>>>> University of Cyprus
>>>>        [[alternative HTML version deleted]]
>>>> 
>>>> 
>>>> ______________________________________________
>>>> R-help@ 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.
>>>> 
>>>> 
>>> 
>>> 
>>> 
>> 	[[alternative HTML version deleted]]
>> 
>> 
>> ______________________________________________
>> R-help@ 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.
>> 
> 
> 
> -----
> Frank Harrell
> Department of Biostatistics, Vanderbilt University
> --
> View this message in context: http://r.789695.n4.nabble.com/kruskal-wallis-post-hoc-tp4288008p4288894.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> 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.

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com