R help - Dec 2007 - How can I extract the AIC score from a mixed model object produced using lmer?

I am running a series of candidate mixed models using lmer (package lme4)
and I'd like to be able to compile a list of the AIC scores for those
models so that I can quickly summarize and rank the models by AIC. When I
do logistic regression, I can easily generate this kind of list by creating
the model objects using glm, and doing:
> md <- c("md1.lr", "md2.lr", "md3.lr")
> aic <- c(md1.lr$aic, md2.lr$aic, md3.lr$aic)
> aic2 <- cbind(md, aic)
but when I try to extract the AIC score from the model object produced by
lmer I get:
> md1.lme$aic
NULL
Warning message:
In md1.lme$aic : $ operator not defined for this S4 class, returning NULL

So... How do I query the AIC value out of a mixed model object created by
lmer?

<<->><<->><<->><<->><<->><<->><<->>
Peter Singleton
USFS Pacific Northwest Research Station
1133 N. Western Ave.
Wenatchee WA 98801
Phone: (509)664-1732
Fax: (509)665-8362
E-mail: psingleton at fs.fed.us

You can calculate the AIC as follows:

(fm1 <- lmer(Reaction ~ Days + (Days|Subject), sleepstudy))
aic1 <- AIC(logLik(fm1))

Hope this helps.
Dave

On 12/18/07, Peter H Singleton <psingleton at fs.fed.us>
wrote:
>
> I am running a series of candidate mixed models using lmer (package lme4)
> and I'd like to be able to compile a list of the AIC scores for those
> models so that I can quickly summarize and rank the models by AIC. When I
> do logistic regression, I can easily generate this kind of list by creating
> the model objects using glm, and doing:
>
> > md <- c("md1.lr", "md2.lr", "md3.lr")
> > aic <- c(md1.lr$aic, md2.lr$aic, md3.lr$aic)
> > aic2 <- cbind(md, aic)
>
> but when I try to extract the AIC score from the model object produced by
> lmer I get:
>
> > md1.lme$aic
> NULL
> Warning message:
> In md1.lme$aic : $ operator not defined for this S4 class, returning NULL
>
> So... How do I query the AIC value out of a mixed model object created by
> lmer?
>
>
<<->><<->><<->><<->><<->><<->><<->>
> Peter Singleton
> USFS Pacific Northwest Research Station
> 1133 N. Western Ave.
> Wenatchee WA 98801
> Phone: (509)664-1732
> Fax: (509)665-8362
> E-mail: psingleton at fs.fed.us
>
> ______________________________________________
> R-help at 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.
>

-- 
David Barron
Said Business School                 Jesus College
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Oxford OX1 1HP                          OX1 3DW
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