[R-sig-ME] (no subject)

[Adam D. I. Kramer]

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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