[R] questions on lme function

[Ana Conesa]

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,
data=clinical)

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
http://bioinfo.cipf.es