Patrick, The likelihoods of two models fitted using REML cannot be compared unless the fixed effects are the same in the two models.
On Tue, 2008-02-26 at 14:38 +0100, Patrick Giraudoux wrote: > Dear listers, > > Here we have a strange result we can hardly cope with. We want to > compare a null mixed model with a mixed model with one independent > variable. > > > lmmedt1<-lme(mediane~1, random=~1|site, na.action=na.omit, data=bdd2) > > lmmedt9<-lme(mediane~log(0.0001+transat), random=~1|site, > na.action=na.omit, data=bdd2) > > Using the Akaike Criterion and selMod of the package pgirmess gives the > following output: > > > selMod(list(lmmedt1,lmmedt9)) > model LL K N2K AIC deltAIC w_i AICc > deltAICc w_ic > 2 log(1e-04 + transat) 44.63758 4 7.5 -81.27516 0.000000 0.65 -79.67516 > 0.000000 0.57 > 1 1 43.02205 3 10.0 -80.04410 1.231069 0.35 -79.12102 > 0.554146 0.43 > > The usual conclusion would be that the two models are equivalent and to > keep the null model for parsimony (!). > > However, an anova shows that the variable 'log(1e-04 + transat)' is > significantly different from 0 in model 2 (lmmedt9) > > > anova(lmmedt9) > numDF denDF F-value p-value > (Intercept) 1 20 289.43109 <.0001 > log(1e-04 + transat) 1 20 31.18446 <.0001 > > Has anyone an opinion about what looks like a paradox here ? > > Patrick > > > > ______________________________________________ > R-help@r-project.org 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. ______________________________________________ R-help@r-project.org 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.
