[R-sig-ME] Comparing mixed models

[Carlos Barboza]

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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