Re: [R] wilcox.test returned estimates

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Thu 16 Feb 2006 - 09:55:34 EST

"Gregory Snow" <Greg.Snow@intermountainmail.org> writes:

> If you really want to look at the difference between 2 medians, then
> consider using permutation tests and bootstrapping for the interval.

Also notice that contrary to popular belief, distributions with identical medians can be significantly different. Simplest example is performance scales where one group scores full marks in 90% of the cases and another group scores full marks in 60% of the cases.  

> -----Original Message-----
> From: r-help-bounces@stat.math.ethz.ch on behalf of pmt1rew@leeds.ac.uk
> Sent: Wed 2/15/2006 4:36 AM
> To: r-help@stat.math.ethz.ch
> Subject: [R] wilcox.test returned estimates
>
> Hi all,
>
> I have being using wilcox.test to test for differences between 2 independent
> samples. I had understood the difference in location to be conventionally the
> difference in the sample medians however this is not the case when implemented
> in R. I have tied ranks and therefore non-exact p-value and confidence
> intervals are calculated due to the normal approximation. But what exactly is
> this normal approximation i.e. how is it involved in estimating the location
> difference?
>
> Further, is it then wrong to refer to the difference in location as the
> difference between the medians? Does anyone have a more appropriate
> description?
>
> Thanks
>
> Rebecca
>
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-- 
   O__  ---- Peter Dalgaard             ุster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)                  FAX: (+45) 35327907

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Received on Thu Feb 16 10:16:21 2006

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