[R ] Query : problems with the arithmetic operator "^" wi th function "lme" and "lmList"

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Hello,

Check also function "AsIs"  ( Usage:  I(x) ).

Regards,
Carlos.

-----Mensaje original-----
De: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] En nombre de Bashir Saghir
(Aztek Global)
Enviado el: mi?rcoles, 07 de mayo de 2003 14:33
Para: 'MARTIN  Ludovic'
CC: 'r-help at stat.math.ethz.ch'
Asunto: RE: [R] [R ] Query : problems with the arithmetic operator "^"
with function "lme" and "lmList"

Dear Martin,

Have you try to create a new variable for age squared, say agesq? If you
fit the model using this new variable you should get the coefficients.
So your new model is something like height~age+agesq

I hope this helps,
Saghir
-----Original Message-----
From:	MARTIN   Ludovic [SMTP:martinl at mathinfo.ens.univ-reims.fr]
Sent:	Wednesday, 07 May, 2003 2:02 PM
To:	r-help at stat.math.ethz.ch
Subject:	[R] [R ] Query : problems with the arithmetic operator
"^"
with function "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 :

 > Oxboys
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.

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