[R] Coding for contrasts in unbalanced designs

Guillaume Brutel guillaume.brutel at yahoo.fr
Tue Apr 3 15:25:14 CEST 2007

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:
 >> 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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 > PLEASE do read the posting guide 
 > and provide commented, minimal, self-contained, reproducible code.

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