Re: [R] Another Mix Model Question

From: Dimitris Rizopoulos <dimitris.rizopoulos_at_med.kuleuven.be>
Date: Tue 21 Jun 2005 - 18:22:31 EST

AFAIK the COVTEST option just computes a Wald test! Since you want test for variance components (which is on the boundary of the parameter space), I'd suggest to use a LRT (i.e., anova.lme(model.1, model.2)) and moreover consider the simulate.lme() function of the "nlme" package.

Best,
Dimitris



Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium

Tel: +32/16/336899
Fax: +32/16/337015
Web: http://www.med.kuleuven.be/biostat/
     http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm


> Hi again,
>
> thank you for your previous answers. Just another question, though
> ...
>
> I get the following variance components after fitting a mixed model.
>
>
> Groups Name Variance Std.Dev. Corr
> PlantID TreatmCtrl 0.51784 0.71961
> TreatmNoAccess 4.77469 2.18511 -0.063
> TreatmNoKeel 4.22726 2.05603 0.513 0.751
> TreatmNoSpur 0.45918 0.67763 0.158 0.303 0.319
> TreatmNoStand 3.45357 1.85838 -0.736 -0.070 -0.435
> 0.495
> PlantID PollClassApis 1.12364 1.06002
> PollClassBombAnth 0.42769 0.65398 -0.759
> Residual 3.09669 1.75974
>
> My question is: if n random effects are included in a model, how can
> I
> test the hypothesis that the variance of such effects is 0 ?
>
> Some sort of COVTEST option in Proc MIXED in SAS (sorry, SAS is
> still
> more familar to me than R).
>
> --
>
> ----------------------------------------------
> Alfonso M. Sanchez-Lafuente
> Departamento de Biologia Vegetal y Ecologia
> Facultad de Biologia
> Universidad de Sevilla
> Avd. Reina Mercedes 9
> E-41012, Sevilla, Spain
> email: alfonso@slafuente.net / slafuente@us.es
>
> ______________________________________________
> R-help@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
>



R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Jun 21 18:25:57 2005

This archive was generated by hypermail 2.1.8 : Fri 03 Mar 2006 - 03:32:55 EST