[R] Why does dredge() rank models differently for lmer() and MCMCglmm()?

[Corina]

Hi Bert,
Thanks for the model selection philosophy! It’s definitely not a perfect world in terms of trying to understand the “truth", but I find that there are so many opinions about how to do model selection that I just choose one and go with it :)

My best,
Corina

-- 
Dr. Corina Logan 
Leverhulme Early Career Research Fellow 
Department of Zoology
University of Cambridge
itsme at CorinaLogan.com 
www.CorinaLogan.com

On Jul 18, 2015, at 21:26, Bert Gunter-2 [via R] <ml-node+s789695n4710033h34 at n4.nabble.com> wrote:

(slightly off topic) 

One might also add that different model fitting criteria might produce 
rankings that are quite different, but with model predictions that are 
very similar. This reflects the inconvenient reality that empirical 
models are merely data interpolators and not representations of 
"truth." Ergo quite different looking models might fit essentially 
equally well, the differences in fits and therefore rankings being 
nothing more than noise. 

Cheers, 
Bert 
Bert Gunter 

"Data is not information. Information is not knowledge. And knowledge 
is certainly not wisdom." 
   -- Clifford Stoll 


On Sat, Jul 18, 2015 at 10:03 AM, Ben Bolker <[hidden email] <x-msg://4/user/SendEmail.jtp?type=node&node=4710033&i=0>> wrote:

> Corina <itsme <at> CorinaLogan.com> writes: 
> 
>> 
>> Hello, 
>> I am running my full model (fm) through lmer() and MCMCglmm() using the 
>> default settings: 
>> 
>> model.lmer <- lmer(fm) 
>> model.MCMCglmm <- MCMCglmm(fm) 
>> 
> 
>   [snip] 
> 
>> However, when I run the models through dredge(): 
>> 
>> dredge(model.lmer) 
>> dredge(model.MCMCglmm) 
> 
>> It ranks the models very differently for lmer() and MCMCglmm() in 
>> the model selection tables, even though I used the default settings 
>> for dredge() as well (ranked by AICc). I would assume the difference 
>> is because lmer() uses REML and MCMCglmm() uses Bayes Rule, however 
>> if this is the case then why weren’t the summary outputs different 
>> as well? 
> 
>   [snip] 
> 
>    This question *might* be better on [hidden email] <x-msg://4/user/SendEmail.jtp?type=node&node=4710033&i=1> ... 
> You shouldn't be comparing models with fixed effects that are fitted 
> with REML -- try  refitting with REML=FALSE.  The model comparison 
> functions in the lme4 package (e.g. anova()) try to stop you from 
> making this mistake, but I'm not sure the MuMIn::dredge does. 
> 
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