[R] AICc in MuMIn package

[Kamil Bartoń]

On 2014-06-27 11:00, r-help-request w r-project.org wrote:
> Date: Thu, 26 Jun 2014 15:12:08 +0200
 > From: Carlos Bautista  Le?n <carlosbautistaleon w gmail.com>
 > To: r-help w r-project.org
 > Subject: [R] AICc in MuMIn package
> Hello, I am modelling in glmmADMB count data
> (I??m using a negative binomial distribution to avoid possitive
> overdispersion) with four fixed and one random effect. I??m also using
> MuMIn package to calculate the AICc and also to model averaging using
> the function dredge. What I do not understand is why dredge calculates a
> different value of the AICc and degrees of freedom than the function
> AICc (please see bellow). Also the logLik changes (as expected).
>> >logLik (glmmadmb.Tot.Pr.nb) ---- 12 in model selection table
> 'log Lik.' -379.739 (df=6)
>> >logLik (glmmadmb.Tot.P.nb)------ 16 in model selection table
> 'log Lik.' -379.688 (df=7)
>
>                              df     AICc
> glmmadmb.Tot.Pr.nb  6   772.8113----12 in model selection table
> glmmadmb.Tot.P.nb   7   775.1825---- 16 in model selection table
>
>
> Model selection table
>       (Int)      Agr/100 Brd/100 Frs/100  HD/100 df   logLik  AICc delta
> weight
> 12 0.90850 -10.570   17.08               1.4220  5 -397.992 806.9  0.00
>   0.713
> 16 1.10300 -10.470   17.39 -0.7603   1.5140   6 -397.730 808.8  1.87  0.280
>
>
> Can anyone explain me why this happend? and which values are correct, those
> from dredge function or those from AICc function?
>
> Thank you very much in advace.
>
> Carlos
>

your models 'glmmadmb.Tot.Pr.nb' and 'glmmadmb.Tot.P.nb' do not seem to
be identical to model '12' and '16', since 'df's do not match (5 and 6
vs 6 and 7). You can compare the model calls to see what differs them:

getCall( glmmadmb.Tot.Pr.nb )
getCall( <model.selection.table> , "12")








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