I am modeling the effects of an environmental variable (X) on fish recruitment (Y) for several, ecologically related species (i) using a mixed-effects model. The linear relationship between X and Y includes a fixed effect that is common across all species and random effects that vary by species. In the lmer() notation from the package lme4: Model<- lmer(Y ~ X +(X|i)) Because the residuals of the model are autocorrelated and the variances differ among species, I would like to include an AR(1) process, and species-specific variances. I have been unable to do this so far in lme4. In the older ?nlme? package, this was possible using: Model<-update (weights=varIdent(form= ~1|i), correlation = corAR1(form = ~ years|i) Is this possible in lme4, and if so, how? Any help would be much appreciated. Cheers, Carrie Holt, Ph.D., M.Sc., B.Sc.(Honours) University of Washington School of Aquatic & Fishery Sciences Box 355020 Seattle, WA 98195 USA
Question on structuring variances using the lme4 package
2 messages · Catherine A. Holt, Dieter Menne
Catherine A. Holt <caholt <at> u.washington.edu> writes:
I am modeling the effects of an environmental variable (X) on fish recruitment
(Y) for several,
ecologically related species (i) using a mixed-effects model. The linear
relationship between X and Y
includes a fixed effect that is common across all species and random effects
that vary by species. In the
lmer() notation from the package lme4: Model<- lmer(Y ~ X +(X|i)) Because the residuals of the model are autocorrelated and the variances differ
among species, I would like
to include an AR(1) process, and species-specific variances. I have been
unable to do this so far in lme4.
In the older ?nlme? package, this was possible using: Model<-update (weights=varIdent(form= ~1|i), correlation = corAR1(form = ~
years|i)
Is this possible in lme4, and if so, how? Any help would be much appreciated. Cheers,
No, it is not (yet) possible. Any reason not use lme? It works, and it is stable, and well documented (Pinheiro/Bates)? lmer is a package in development, it has been made public mainly to provide feedback to the author, Douglas Bates. See also the special list http://news.gmane.org/gmane.comp.lang.r.lme4.devel Dieter