[R-sig-ME] help random effects unested

[Andrew Robinson]

Hi Maria,

it sounds like you would like those factors to be crossed.  It is possible
to cross factors within lme but it is not easy - you might find some
guidelines searching R-help via Google.  Alternatively you could try to
use the lmer() function within the lme4 package, this function allows you
to cross random effects.

I hope that this helps,

Andrew

On Sat, June 28, 2008 2:13 am, Maria Eva Gongora wrote:
>
> I am using mixed effect models (library nlme, lme) to evaluate  factors
> that influence bycatch of hake in a shrimp fishery. Data are collected
> though an on-board observer program and  I decided to treat the vessel id
> and the observer id as random effects. A priori I would expect the
> observer effect to be independent of  vessel.  However, I did not find a
> way to incorporate both factors as independent, unnested random effects; I
> could only estimate the effects as “vessel” and “observer in vessel”
> (nested).
>
> Is it possible  to incorporate two random effects unested?
>
> Lic. María Eva Góngora
>
>
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Andrew Robinson
Senior Lecturer in Statistics                       Tel: +61-3-8344-6410
Department of Mathematics and Statistics            Fax: +61-3-8344 4599
University of Melbourne, VIC 3010 Australia
Email: a.robinson at ms.unimelb.edu.au    Website: http://www.ms.unimelb.edu.au