Re: [R] Coding for contrasts in unbalanced designs

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Tue 03 Apr 2007 - 17:20:02 GMT

Guillaume Brutel wrote:
> In fact I want to test for the effects of multiple continuous and
> categorical variables (with GLMs) which are nested in the factor levels
> on a single continuous variable. Since the design is unbalanced, I
> though I had to specify it in the glm formula.
>
>
That didn't make me any wiser... What is the model and which hypotheses do you wish to test?
>
> Guillaume Brutel wrote:
> > Sorry for possible cross posting but it seems that my previous
> message was send as HTML and then scrubbed.
> >
> > Dear list members,
> >
> > I want to use a GLM with an unbalanced factor and continuous variables.
> > My factor F has 12 unbalanced levels:
> >
> F=as.factor(c('A','B','C','C','C','C','D','D','D','D','D','D','E','E','E','E','E','E','F','G','G','H','I','I','J','J','J','K','L','L','L'))
> >
> >> summary(F)
> >>
> > A B C D E F G H I J K L
> > 1 1 4 6 6 1 2 1 2 3 1 3

> >
> > I thus want to code contrasts appropriatly.
> > I have looked in R documentations and R-help archives without finding
> the information for unbalanced designs.
> > Any help will be very useful.
> > Thanks you very much.
> > Guillaume Brutel.
> >
> >
> Er, in which sense do you mean "code contrasts"? There are some
> ambiguities relating to the use of the term "contrasts", so it isn't
> possible to tell what it is that you need. Please give an example of
> what you want to do and explain why you think that it night come out
> wrong when data are unbalanced.
>



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