From: JRG <loesljrg_at_verizon.net>

Date: Tue 15 Mar 2005 - 06:38:10 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Mar 15 03:40:15 2005

Date: Tue 15 Mar 2005 - 06:38:10 EST

On 14 Mar 2005 at 17:22, Peter Dalgaard wrote:

> "JRG" <loesljrg@verizon.net> writes:

*>
**> > On 14 Mar 2005 at 16:13, Peter Dalgaard wrote:
**> >
**> > > Alice Le Bars <alice.le-bars@nantes.inserm.fr> writes:
**> > >
**> > > > Dear all,
**> > > >
**> > > > I would be glad if someone could tell me if Tukey HSD (function of
**> > > > stats library) accept the NA values and could correct the unbalanced
**> > > > design (different number of sample in each group)
**> > >
**> > > I don't think the *theory* of the HSD allows this. There is some more
**> > > or less well-founded speculation that if the imbalance is not too bad,
**> > > then the HSD results are somewhat useful anyway, but please consider
**> > > using the multcomp package, which is specifically designed to get
**> > > these things right.
**> > >
**> >
**> > I believe that Hayter (JASA, 1984, 12, 61--75) proves that the so-called Tukey-Kramer method is guarnateed to be conservative for
**> > any set of cell sizes --- under the usual ANOVA model, of course.
**>
**> Make that Annals of Statistics, not JASA.
**>
**> Hayter proves that simultaneous confidence intervals based on using
**> the Studentized range distribution with (1/ni+1/nj)/2 instead of 1/n
**> will have coverage at least (1 - \alpha). He doesn't say *how*
**> conservative it is, though, and it doesn't change the fact that
**> multcomp has a better idea.
**>
*

Whoops, let it be Annals. However, there is a paper by Dunnett (ca 1981) which I again believe to be JASA which shows that the degree of conservativism is pretty slight, over a broad range of cell sizes. Your point about multcomp stands.

**---JRG
**

*> --
*

> O__ ---- Peter Dalgaard Blegdamsvej 3

*> c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
**> (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
**> ~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907
*

John R. Gleason

Associate Professor

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R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Mar 15 03:40:15 2005

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