Re: [R] Extracting overdispersion estimates from lmer amd glm objects

From: David Barron <mothsailor_at_googlemail.com>
Date: Tue 12 Sep 2006 - 08:26:54 GMT

PS, the equivalent for a glm is:

> sum.modeltest <- summary(modeltest)
> sum.modeltest$dispersion

Hope this helps.

On 11/09/06, Toby Gardner <t.gardner@uea.ac.uk> wrote:
> Dear list,
>
> I am needing to extract the estimate of overdispersion (deviance / residual degrees of freedom or c-hat) from multiple model objects - so they can then be used to compare the extent of overdispersion among alternative models as well as calculate qausi-AIC values. I have been unable to do this, despite consulting a number of manuals and searching the R-help. I am imaging that in theory it should be possible with some call to attr(), but i have so far had no success.
>
> An example model output would be:
>
> > modeltest<-lmer(Coleodactylus_amazonicus_N~USD + (1|site),data=SFArray,family=poisson,method="Laplace",control=list(usePQL=FALSE, msVerbose=TRUE))
> > summary(modeltest)
>
> ------------
>
> Generalized linear mixed model fit using Laplace
> Formula: Coleodactylus_amazonicus_N ~ USD + (1 | site)
> Data: SFArray
> Family: poisson(log link)
> AIC BIC logLik deviance
> 75.94996 81.68603 -34.97498 69.94996
> Random effects:
> Groups Name Variance Std.Dev.
> site (Intercept) 2.6076 1.6148
> number of obs: 50, groups: site, 5
>
> Estimated scale (compare to 1) 1.080798
>
> ------------
>
> What I need is to extract this value (1.080798) from multiple lmer objects. Has anyone any recommendations? I also need to do this for glm objects although I suspect if someone was able to kindly point me in the right direction then the solution is likely to be similar.
>
> Very many thanks,
>
> Toby Gardner
>
> > sessionInfo()
> Version 2.3.1 (2006-06-01)
> i386-pc-mingw32
>
> attached base packages:
> [1] "datasets" "graphics" "grDevices" "methods" "stats" "utils" "base"
>
> other attached packages:
> JGR iplots JavaGD lme4 Matrix lattice MASS rJava
> "1.4-7" "1.0-3" "0.3-4" "0.995-2" "0.995-15" "0.13-8" "7.2-27.1" "0.4-6"
>
>
> School of Environmental Sciences
> University of East Anglia
> Norwich, NR4 7TJ
> United Kingdom
> Email: t.gardner@uea.ac.uk
> Website: www.uea.ac.uk/~e387495
>
> [[alternative HTML version deleted]]
>
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>

-- 
=================================
David Barron
Said Business School
University of Oxford
Park End Street
Oxford OX1 1HP

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Received on Tue Sep 12 18:32:38 2006

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