[R] Coding for contrasts in unbalanced designs

From: Guillaume Brutel <guillaume.brutel_at_yahoo.fr>
Date: Tue 03 Apr 2007 - 13:25:14 GMT


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.

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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Received on Tue Apr 03 23:30:38 2007

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