[R] posthoc tests with ANCOVA

[Walter Durka]

dear all,

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"

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?

Thanks for any comments
Walter


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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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Das UFZ hat einen neuen Namen:
Helmholtz-Zentrum für Umweltforschung GmbH - UFZ

The UFZ has a new name:
Helmholtz Centre for Environmental Research - UFZ

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