[R] lme: random effects of a quadratic term

[Prof Brian Ripley]

On Sat, 26 Mar 2005, Montse Rue wrote:

> Thanks! I already tried it, but then I have problems with the augPred
> values. I get straight lines instead of quadratic lines when plotting
> the augPred values.
>
> What can I do?

WHy are you expecting a non-linear plot from a linear fit?

> Montse
>
>
> On Sat, 26 Mar 2005 09:39:07 +0000 (GMT), Prof Brian Ripley
> <ripley at stats.ox.ac.uk> wrote:
>> On Sat, 26 Mar 2005, Montse Rue wrote:
>>
>>> I am estimating the following model:
>>>
>>> so2.lme<-lme(so2~1+I(alcadakm^2)+dia,data=subjectes2,na.action=na.omit)
>>>
>>> And when I try to plot the random effects of the quadratic term with
>>> respect to a covariate (mam) I get an error:
>>>
>>>> so2.lmeRE<-ranef(so2.lme,augFrame=T)
>>>> plot(so2.lmeRE,form=I(alcadakm^2)~mam)
>>> Error in plot.ranef.lme(so2.lmeRE, form = I(alcadakm^2) ~ mam ) :
>>>       Only single effects allowed in left side of form.
>>>
>>> Any suggestion?
>>
>> Try renaming the variable, e.g. alcadakm2 = alcadakm^2, and refit.
>>
>> NB: this is not `a quadratic term' but a transformed variable, since you
>> used I().
>>
>> --
>> Brian D. Ripley,                  ripley at stats.ox.ac.uk
>> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
>> University of Oxford,             Tel:  +44 1865 272861 (self)
>> 1 South Parks Road,                     +44 1865 272866 (PA)
>> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>>
>
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595