[R] posthoc tests with ANCOVA

[Torsten Hothorn]

On Tue, 9 Jan 2007, Walter Durka wrote:

> dear all,
>

Walter,

_please_ cc questions on contributed packages to the maintainer, since not 
everybody follows r-help closely...

> I want to perform a posthoc test for my ANCOVA:
> a1<-aov(seeds~treatment*length)
>
> With
> summary(glht(a1, linfct = mcp(treatment = "Tukey")))
> R tells me: "covariate interactions found -- please choose appropriate
> contrast"
>

one needs to specify a certain value for `length' which, I assume, is a 
numeric covariate, right? The current interface doesn't support this (this 
on my to-do-list), however, you can set up the matrix of linear functions 
by yourself (contact me privately if you have problems to do that).

> How do I build these contrasts?
>
> Ideally, I would like to have the posthoc test for the ANCOVA including
> a block-effect
> a2<-aov(seeds~treatment*length+Error(site))
>
> How do I make a posthoc test here?
>

its on the to-do-list as well :-(

Torsten

> Thanks for any comments
> Walter
>
>
> -- 
>
> *****
> Dr. Walter Durka
> Department Biozönoseforschung
> Department of community ecology
>
> Helmholtz-Zentrum für Umweltforschung GmbH - UFZ
> Helmholtz Centre for Environmental Research - UFZ
> Theodor-Lieser-Str. 4 / 06120 Halle / Germany
>
> walter.durka at ufz.de / http://www.ufz.de/index.php?en=798
> phone +49 345 558 5314 / Fax +49 345 558 5329
>
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