[R] questions on lme function

[Dr Ross Darnell]

Ana

You are estimating a random coefficient model on 5 individuals (mean 
and variance). Are you sure this is wise?

Ross Darnell 

----- Original Message -----
From: Ana Conesa <aconesa at ochoa.fib.es>
Date: Thursday, July 5, 2007 1:21 am
Subject: [R] questions on lme function
> 
> 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
> 
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