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
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