Re: [R] stratified Wilcoxon available?

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Tue 30 Aug 2005 - 23:46:44 EST

torsten@hothorn.de writes:

> > Nice to see that the old code made sense.
>
> Nice to see that the new code is working correctly :-)
>
> > A bit surprising that it
> > gives _exactly_ the same result as the blockwise ranking in coin...
>
> why? Without ties, the conditional and unconditional versions of the tests
> should have exactly the same result.

Oh, just that there are a number of little things that could have been done in slightly different but asymptotically equivalent ways. The scale factor for the within-block ranks e.g.  

> > Perhaps introduce some ties? (round(y,1) is usually effective).
> >
>
> this should generate differences, yes.
>
> > The trend test is easily fixed: just spell "t value" without capital V
> > as we do nowadays. This gives
> >
> >
> > > SKruskal.test(y ~ x | b, data = mydf, trend = TRUE)
> >
> > Kruskal-Wallis stratified rank sum trend test
> >
> > data: y , group: x , strata: b , trend: as.numeric(group)
> > Z = -0.1624, df = 1, p-value = 0.871
> >
> > > SKruskal.test(y ~ x | b, data = mydf, trend = 1:3)
> >
> > Kruskal-Wallis stratified rank sum trend test
> >
> > data: y , group: x , strata: b , trend: 1 2 3
> > Z = -0.1624, df = 1, p-value = 0.871
> >
> > (The df=1 is a bit misleading in this case...)
> >
>
> maybe report 0.1624^2 = 0.0264 as test statistic (same as with teststat
> = "quad" in `coin')?

Yes, but there was a point in getting a signed statistic. Otherwise, I might as well have reused the code that used the SSD from the anova table.

-- 
   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 Tue Aug 30 23:51:57 2005

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