lme: random effects of a quadratic term

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?

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)
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