Sent: Wednesday, May 07, 2003 7:02 AM
To: r-help at stat.math.ethz.ch
Subject: [R] [R ] Query : problems with the arithmetic
operator "^" withfunction "lme" and "lmList"
Dear all,
I've got a problem in including square variables in lme and lmlist
functions. I've tried to work on Oxboys data of Pinheiro and
Bates'book, which consist of the heights of 26 boys, each mesured on
nine different occasions :
Grouped Data: height ~ age | Subject
Subject age height Occasion
1 1 -1.0000 140.50 1
2 1 -0.7479 143.40 2
3 1 -0.4630 144.80 3
4 1 -0.1643 147.10 4
5 1 -0.0027 147.70 5
...
A quadratic model in "age" would be fit with lmList
(height~age+age^2,Oxboys).
We obtain:
fm2Oxboys.lis<-lmList(height~age+age^2,Oxboys)
fm2Oxboys.lis
Call:
Model: height ~ age + age^2 | Subject
Data: Oxboys
Coefficients:
(Intercept) age
10 130.2616 3.722915
26 137.9927 5.588783
25 139.2105 4.024081
9 138.1369 6.009057
2 142.8584 5.440176
...
19 164.5761 9.065620
4 165.0724 9.360561
Degrees of freedom: 234 total; 182 residual
Residual standard error: 0.6598878
They are not coefficients associated with the covariate "age^2" !
However, the model called is " Height~age+age^2 | Subject " .
I would be grateful if anyone could help me.
Cordially,
Martin Ludovic.