[R] Type II ANOVA for user-defined contrasts with covariates

[John Fox]

Dear Jordan,

Oddly, essentially the same question was posed by someone else three days ago.

Because groups enters the model additively, the proper test for each contrast is just the t-test for the corresponding coefficient in the summary()  for the model.

I hope this helps,
 John

------------------------------------------------
John Fox
Sen. William McMaster Prof. of Social Statistics
Department of Sociology
McMaster University
Hamilton, Ontario, Canada
http://socserv.mcmaster.ca/jfox

On Mon, 9 Jul 2012 20:06:22 +0100
 Jordan Ramsey <jmr201 at cam.ac.uk> wrote:
> I'm wondering if anyone would be able to help me out. I'm trying to use a
> type II ANOVA for a model with user-specified contrasts and covariates.
> 
> I have two treatment groups and a control group. I'm comparing average
> treatment to controls and also between the two treatment groups, but I'm
> also looking to adjust for age and gender as covariates:
> 
> contrastMat=cbind(c(-1,-1,2),c(1,-1,0))
> contrasts(groups)=contrastMat
> 
> Model=lm(Response~Age+Gender+Age:Gender+groups)
> 
> since I'm interested in SS(R | A,G,AG)
> 
> I was hoping then to use the Anova() function in the car() package to find
> the type II ANOVA for my specified contrasts, but when I do so it only
> looks at Response as a whole instead of the two contrasts. Any ideas where
> I'm going wrong?
> 
> Thanks,
> JR
> 
> 	[[alternative HTML version deleted]]
> 
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