[R] questions on lme function

Ana Conesa aconesa at ochoa.fib.es
Wed Jul 4 17:21:53 CEST 2007

Dear list,

I am using the lme funcion to fit a mixed model for the time response
of a number of physiological variables. The random variable would be
the individual on which physiological variables are measured at
different time points. I have 4 time points, 5 individuals and 3
replicates per condition (time/individual),  and I would like to fit
a quadratic model on time. The model I am using is

> mm <- lme(myvar ~ time + time2, random= ~ time|individual,

being time2 = time*time

I have a number of questions

1) I am not very sure the random effect is correctly modeled. Would I
need to include the time2 variable aswell?

2) I would like to extract the F statistics of the model, and I do
not find a function for this. Is this possible?

3) depending of the variable I take, I frequently obtain a
convergence error as a result of the lme funcion. Any ideas on what
to do to improve convergence?

Thank you

Ana Conesa, PhD
Centro de Investigacion Principe Felipe
Avda. Autopista Saler 16 46013 Valencia

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