Dear all specialist users of S+,
I had to use the following code :
> W.lme <- lme(Value ~ Treatment*ordered(TimeNumber), random = ~1 | Rat,
data = W)
to analyse the so-called "Value", with "TimeNumber" refering to a repeated
measurement design (2 different days of evaluation), and "Treatment" being a
factor variable with 3 levels, say X (coded 1), Y (coded 2) and Z (coded 3).
"Rat" is the subject (different set of subjects in the three treatment
groups).
The output gave me the following results :
Value Std.Error DF t-value p-value
Treatment1 -3.59722 1.128908 15 -3.18646 0.0061
Treatment2 -0.78241 0.651775 15 -1.20042 0.2486
So I was left with the interpretation of what "Treatment1" and "Treatment2"
means ?
I investigated the different outputs produced by "lme" in such a case, by
changing the coding of the treatment levels. For example, I set X = 2, Y =
3, Z = 1, and so on for all the 6 possibilites. From what I obtained, I came
to the interpretation that :
"Treament1" refers to the comparison of the level coded 2 with the level
coded 1
"Treatment2" refers to the comparison of the level coded 3 with the other
levels 1 and 2 as a whole.
Can anybody tell me if this is the right interpretation ?
Andre Mery
Biostatistics Departement
Aventis Pharmaceuticals
102, route de Noisy
93235 Romainville Cedex
France
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