[R] Redundancy contrasts
Robert.Espesser at lpl.univ-aix.fr
Tue Feb 18 11:12:03 CET 2003
Is it meaningful to run 2 different sets of contrasts on a model , or is
there some redundancy somewhere ?
For example,I have a model :
tcons ~ group
where group is a factor with 3 levels ( A, B, C)
I first run the model with the default contrasts (treatment),
so I tested (A vs B) and (A vs C);
but is it meaningful to also carry on a 2nd analysis with an other set
contrasts, to test B vs C ? ie c(0,-1,1) , in fit.contrasts
I'v heard that the first set of contrast ( ie treatment default in
extracts all the "information"
in the model, and that a second analysis with an other set of contrasts
was not meaningful.
Thanks for help.
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Tel: +33 (0)4 42 95 36 26 Fax: +33 (0)4 42 59 50 96
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