(no subject)
Hi Lawrence, contrasts(lambweight$age) returns the contrast matrix that is tested by lm, lme, etc....you can assign to this matrix. You probably want contrasts(lambweight$age) <- matrix(c( 1,0,0, 0,1,0),nrow=2) ...to do it in lme proper, add contrasts=list(age=matrix(c(1,0,0,0,1,0),nrow=2)) to your command line. Note also that you're not getting estimates for age2 and 3, you're getting estimates for the difference between age2 and age1, and between age3 and age1. --Adam
On Tue, 27 Jan 2009, Lawrence Lee wrote:
Dear all,
Does anyone know how to change the reference group within lme().
For example,
lme(fixed = obs ~ line + age - 1,random = ~1 |sire, data = lambweight)
Suppose age has 3 levels, so the code above will give me estimate
of age2 and age3:
Fixed effects: obs ~ line + age - 1 Value Std.Error DF t-value
p-valueline1 10.491153 0.7261881 18 14.446882 0.0000line2 12.290287
0.8242309 18 14.911219 0.0000line3 11.032864 0.7647870 18 14.426061
0.0000line4 10.276735 0.7389137 18 13.907897 0.0000line5 10.952840 0.6084109
18 18.002373 0.0000age2 -0.155435 0.7157030 38 -0.217178 0.8292age3
0.009646 0.5481034 38 0.017599 0.9861
How I can change within lme() in order to give me the estimate of
age1 and age2.
Thanks,
Lawrence
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