Re: [R] Mixed model question

From: Spencer Graves <>
Date: Sat 18 Jun 2005 - 01:43:41 EST

          Have you also tried "lmer" in library(lme4)? This is newer and better in many ways. Unfortunately, I see only one example in the Help file, but you might be able to figure out how to use lmer from the help file and from the 125 hits on RSiteSearch("lmer").

          The definitive work on this subject, from my perspective, is Pinheiro and Bates (2000) Mixed-Effects Models in S and S-PLUS (Springer). This book is primarily how to use lme. I learned a lot from it (and from Doug Bates' other book with Don Watts on nonlinear regression). I couldn't find Pinheiro and Bates in the catalog for the library at Universidad de Sevilla (though Bates and Watts was listed).

          Feel free to submit other questions after you've considered this, but PLEASE do read the posting guide! first. In particular, you might have gotten a more helpful reply to this question if you had included one of your attempts with "lme", asking what you did wrong or what you don't understand about the results.

	  Buena suerte,
	  spencer graves

Alfonso M Sanchez-Lafuente wrote:
> Hi,
> I am new to this list as a poster, but a reader for some time.
> I've using R for several weeks now, and I have a lot of questions about
> certain procedures. Here I go:
> I want to test if there are differences in the time spent by pollinators
> visiting flowers of a given plant species, according to a number of
> experimental manipulations made on those flowers. All experimental
> manipulations (factor with 5 levels) are replicated within plants (i.e.
> plant is my sampling unit). Further, I have two populations (two level
> factor), and a number of pollinator groups (again, two levels, the same
> in both populations). The response variables in the numbe of seconds
> invested in each probe. Further, I have plant floral display as a
> covariate, as it may influence visitation rates.
> I think I have to analyse this desing considering population, pollinator
> group and their interaction as fixed effects, and treatment nested
> within plant, and its interaction with population and pollinator group,
> as random factors.
> In SAS terminology, the model looks like this:
> proc mixed data=flwfunc.visitflower covtest method=reml;
> class site pollclass treatm plantid;
> model time = site|pollclass flwinflor / chisq;
> random treatm site*treatm pollclass*treatm / subject=plantid;
> lsmeans site pollclass site*pollclass;
> run;
> I've been successfully trying lm, but I think is not suitable for random
> effects. Thus, I've tried lme, but no success when defining the random
> part or trying to interpret the results...
> Any help will be welcome!
> mailing list PLEASE do read the posting guide! Received on Sat Jun 18 03:18:00 2005

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