[R] anova with models from glmmPQL

[Lorenz.Gygax@fat.admin.ch]

> I try to compare some models obtained from glmmPQL.
>  
> model1 <-
> glmmPQL(y~red*yellow+I(red^2)+I(yellow^2)+densite8+I(densite8^
> 2)+freq8_4
> +I(freq8_4^2), random=~1|num, binomial);
> model2 <-
> glmmPQL(y~red*yellow+I(red^2)+I(yellow^2)+densite8+I(densite8^
> 2)+freq8_4
> , random=~1|num, binomial);
> anova(model1, model2)

You try to compare models that differ in their fixed parts. This is not
possible with the default method 'REML'. This would only be possible if you
fitted your models using method 'ML' (see Pinheiro & Bates, 2000).

In addition, if I understood a remark by José Pinheiro during one of his
courses correctly, the anova comparisons are not save with a distribution
other than normal. Thus, one should rely on the function intervals () to see
whether confidence intervals of the parameters overlap zero or not. Perhaps
someone else can comment on this issue?

Regards, Lorenz
- 
Lorenz Gygax
Centre for proper housing of ruminants and pigs
Swiss Federal Veterinary Office
agroscope FAT Tänikon, CH-8356 Ettenhausen / Switzerland