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 ----- Original Message ----- From: "Alfonso M Sanchez-Lafuente" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, June 21, 2005 9:57 AM Subject: [R] Another Mix Model Question > 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: [EMAIL PROTECTED] / [EMAIL PROTECTED] > > ______________________________________________ > [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 > ______________________________________________ [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
