I agree with Bert. The lme() helper functions are much more developed than the lmer() helper functions. This is probably relevant for Simon's data because temporal autocorrelation is likely for the measurements within chicks, and is easily handled in lme(). I'm not sure if it can be done yet in lmer().
Cheers Andrew On Tue, Sep 05, 2006 at 09:14:20AM -0700, Berton Gunter wrote: > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Andrew Robinson > > Sent: Tuesday, September 05, 2006 7:25 AM > > To: Simon Pickett > > Cc: [email protected] > > Subject: Re: [R] help: advice on the structuring of ReML > > models foranalysing growth curves > > > > Hi Simon, > > > > overall I think that lmer is a good tool for this problem. It's > > impossible to reply definitively without the full details on the > > experimental design. > > > > Caveat in place, I have questions and some suggestions. Are > > treatment1 and treatment2 distinct factors, or two levels of a > > treatment, the dietary compound? Also, what is broodsize? > > > > If you want to nest chick id within brood, I think that you should > > include the interaction as a random factor. If you'd like the age > > effects to differ between chicks then age should be on the left of id. > > > > Thus, start with something like ... > > > > model1 <- lmer(weight ~ treatment + broodsize + sex + age > > + (1|brood) + (age|id:brood), data=H) > > > FWIW, this model can also be easily fit with the lme() function (in the nlme > package) as the random effects are strictly nested. The only advantage in > doing so is that the lme tools for examining the model are somewhat more > developed and extensive (or am I just more familiar with them?) > > Cheers, > Bert > > - Bert Gunter > Genentech Non-Clinical Statistics > South San Francisco, CA > > "The business of the statistician is to catalyze the scientific learning > process." - George E. P. Box -- Andrew Robinson Department of Mathematics and Statistics Tel: +61-3-8344-9763 University of Melbourne, VIC 3010 Australia Fax: +61-3-8344-4599 Email: [EMAIL PROTECTED] http://www.ms.unimelb.edu.au ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
