[R] Help with contrasts

Paschal
2009-01-07T08:48:16Z

Hello All R Gurus

I'm a relatively new user to R and I'm having so problems fully grasping
the
contrasts notion. So any help will be appreciated.
Lately I've been playing around with lme and I was looking at the help files
of anova.lme where there is this example


options(contrasts = c("contr.treatment", "contr.poly"))
fm1BW.lme <- lme(weight ~ Time * Diet, BodyWeight,
                   random = ~ Time)
fm2BW.lme <- update(fm1BW.lme, weights = varPower())
# Test a specific contrast
anova(fm2BW.lme, L = c("Time:Diet2" = 1, "Time:Diet3" = -1))

after running it I get the following result

F-test for linear combination(s)
Time:Diet2 Time:Diet3
         1         -1
  numDF denDF  F-value p-value
1     1   157 2.862598  0.0926

My question is how can I test for the Time:Diet1 interaction term and
compare all three diets.

Best regards,
Paschal

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