R help - May 2011 - unbalanced anova with subsampling (Type III SS)

Hello R-users,
I am trying to obtain Type III SS for an ANOVA with subsampling. My design
is slightly unbalanced with either 3 or 4 subsamples per replicate.

The basic aov model would be:
fit <- aov(y~x+Error(subsample))

But this gives Type I SS and not Type III.

But, using the drop() option:
drop1(fit, test="F")

I get an error message:
"Error in UseMethod("extractAIC") : no applicable method for
"extractAIC"

Changing the "contrasts" to "contr.helmert",
"contr.poly" also does not
help.

Can I use library(car) for unbalanced subsamples?

I am very confused.
Any help would be greatly appreciated.
-Sam

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Dear Sam,

I don't think that you can use the Anova() function in the car package for
this design because there would be no way to specify the error term.

Sorry,
 John

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


> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org]
> On Behalf Of Sam Chand
> Sent: May-20-11 11:15 PM
> To: r-help at r-project.org
> Subject: [R] unbalanced anova with subsampling (Type III SS)
> 
> Hello R-users,
> I am trying to obtain Type III SS for an ANOVA with subsampling. My 
> design is slightly unbalanced with either 3 or 4 subsamples per 
> replicate.
> 
> The basic aov model would be:
> fit <- aov(y~x+Error(subsample))
> 
> But this gives Type I SS and not Type III.
> 
> But, using the drop() option:
> drop1(fit, test="F")
> 
> I get an error message:
> "Error in UseMethod("extractAIC") : no applicable method for
> "extractAIC"
> 
> Changing the "contrasts" to "contr.helmert",
"contr.poly" also does
> not help.
> 
> Can I use library(car) for unbalanced subsamples?
> 
> I am very confused.
> Any help would be greatly appreciated.
> -Sam
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting- 
> guide.html and provide commented, minimal, self-contained, 
> reproducible code.

On 21/05/11 15:15, Sam Chand wrote:
> Hello R-users,
> I am trying to obtain Type III SS for an ANOVA with subsampling. My design
> is slightly unbalanced with either 3 or 4 subsamples per replicate.
>
> The basic aov model would be:
> fit<- aov(y~x+Error(subsample))
>
> But this gives Type I SS and not Type III
<SNIP>

You ***really should*** have a look at

    www.stats.ox.ac.uk/pub/MASS3/Exegeses.pdf


cheers,

         Rolf Turner


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