[R-sig-ME] Comparing mixed models

[Carlos Barboza]

yes I agree, my question was just a numerical doubt about comparing AIC
values. My approach was to show that, the AIC value from a model including
the single fixed effect has a smaller AIC value than any other model only
including the interecept effect in the fixed structure

thank you

2016-05-07 12:34 GMT-03:00 Ben Bolker <bbolker at gmail.com>:

>
>   My only other comment would be that my standard approach would be to
> retain all random effects in the model unless they are causing difficulty
> in model fitting -- this depends on your goal (confirmation/testing,
> prediction, exploration)
>
> On Sat, May 7, 2016 at 11:26 AM, Carlos Barboza <carlosambarboza at gmail.com
> > wrote:
>
>> Dear Dr. Ben Bolker
>>
>> My name is Carlos Barboza and I am a Marine Biologist from the Rio de
>> Janeiro University, Brazil. First it's a pleasure to again have the
>> opportunity to send you a message.The reason for it is a simple doubt:
>> Can I compare AIC from:
>>
>> 1. glmmADMB: Density ~ 1 + 1|Site
>>
>> 2. glmmADMB: Density ~ Sector + 1|Site + Cage
>>
>> Note that they have different random and fixed structures. I know that
>> this is not the best choice to model selection but, I think that the AIC
>> values can be compared.
>>
>> thank you very much for your attention
>>
>>
>>   is Cage a random effect?  Are you intentionally leaving out the
>> intercept in the second case (it will be included anyway unless you
>> use -1)?  In any case, I don't see any obvious reason you can't
>> compare AIC values; see
>>
>> https://rawgit.com/bbolker/mixedmodels-misc/master/glmmFAQ.html#can-i-use-aic-for-mixed-models-how-do-i-count-the-number-of-degrees-of-freedom-for-a-random-effect
>>
>>   Follow-ups to r-sig-mixed-models at r-project.org, please ...
>>
>> sorry, yes, cage was included only to examplify a different random
>> structure in the second case...it should be coded (1|Site) + (1|Cage)
>> yes, I know that the intercept will be included in the second model
>>
>> it's an example of comparing AIC values from mixed models with different
>> fixed and random structures:
>>
>> 1. Density ~ 1 + 1|Site
>>
>> 2. Density ~ Sector + 1|Site + 1|Cage
>>
>> comparing AIC...I beleive that both values can be compared
>>
>> again, thank you very much for your very fast message
>>
>>
>>
>>
>

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