Re: [R] Anova with Scheffe Tests

From: Simon Blomberg <Simon.Blomberg_at_anu.edu.au>
Date: Wed 02 Mar 2005 - 11:24:59 EST

Hi,

I don't think there are any packages on CRAN that implement Scheffe's test. If you don't mind using another multiple comparisons procedure, you could look at ?TukeyHSD and/or the multcomp package. Alternatively, you could write your own function to do Scheffe's test. At least one other person has done that. See the following post in the R-help archive
http://finzi.psych.upenn.edu/R/Rhelp02a/archive/19393.html. I can't vouch for whether that person's function works properly, but it shouldn't be hard to hand-check it, and improve it. You could search R-help yourself and maybe come up with other solutions.

Cheers,

Simon.

>Hi R-people,
>
>I am wanting to run Factorial ANOVA followed by Scheffe tests on
>some spatial subjective data. I'm comparing X-Y independent
>coordinates against x-y dependent coordinates. There are only four
>independent spatial coordinates that form a square.
>
>I am wondering whether I am doing the right thing, because there
>doesn't seem to be a simple way of doing this. I have attempted to
>read `Practical regression and ANOVA using R' and am still confused.
>
>In good ol' Statview (now dearly departed) to complete a Scheffe
>test you selected the independent variables and dependent variable
>and it produced a table with the pairwise comparisons of the levels
>of the factor. I'm looking for a system that is as basic, but can be
>done using R and has documentation so I'm not guessing what I'm
>doing. I'd rather not have to do plots in R and then run over to
>dead software to do Scheffe's if possible.
>
>I checked on google and there seems to be code for a couple of
>functions out there, but I need something that has a manual.
>
>Is there a Scheffe function out there that is reasonably well
>documented, or should I consider some other method of dealing with
>this data. We have been using Scheffe for this type of analysis as I
>was under the impression it was very conservative. Tukey's HSD seems
>to be conservative as well. Should I try this? Is there a different
>approacch that is better and where can I read about it.
>
>Thanks for any help you can provide.
>
>Sam
>
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-- 
Simon Blomberg, B.Sc.(Hons.), Ph.D, M.App.Stat.
Visiting Fellow
School of Botany & Zoology
The Australian National University
Canberra ACT 0200
Australia

T: +61 2 6125 8057  email: Simon.Blomberg@anu.edu.au
F: +61 2 6125 5573

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Received on Wed Mar 02 11:52:55 2005

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