The lme4 package is still in development. I can't guarantee the evaluation of the deviance for the quasipoisson family. There is a certain amount of mystery about the role of the dispersion parameter and the null deviance in families like quasipoisson and quasibinomial. For the time being don't base tests on a value of the deviance for such models.
On Feb 20, 2008 8:19 AM, Martijn Vandegehuchte <[EMAIL PROTECTED]> wrote: > Dear R-users, > > I am currently trying to switch from SAS to R, and am not very familiar with > R yet, so forgive me if this question is irrelevant. > > If I try to find the significance of the fixed factor "spikes" in a > generalized linear mixed model, with "site" nested within "zone" as a random > factor, I compare following two models with the anova function: > > model1<-lmer(aphids~spikes+(1|zone:site), method="ML", family=quasipoisson) > model2<-lmer(aphids~(1|zone:site), method="ML", family=quasipoisson) > anova(model1,model2) > > This gives me a p< 2.2e-16 ***, concluding that "spikes" has a highly > significant effect on "aphids". However, when I look at the summary of model1: > > summary(model1) > > I find a t-value for "spikes" of -0.1166 which is really insignificant... > > When I try model1 in SAS with proc glimmix, corrected for overdispersion with > "random _residual_", it also gives a p-value for "spikes" of 0,985. So if > "spikes" is not having a significant effect on "aphids", then why the above > mentionned p-value generated by anova in R? > > Can anyone explain this? > > Please find the dataset in the attachment. > > Many thanks beforehand, > > Martijn. > > > > > > > > > > -- > Martijn Vandegehuchte > Ghent University > Department Biology > Terrestrial Ecology Unit > K.L.Ledeganckstraat 35 > B-9000 Ghent > telephone: +32 (0)9/264 50 84 > e-mail: [EMAIL PROTECTED] > > website TEREC: www.ecology.ugent.be/terec > > ______________________________________________ > 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.
