[R-sig-ME] Comparing mixed models

Ben Bolker bbolker at gmail.com
Sat May 7 17:34:30 CEST 2016


  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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