Comparing mixed models

Dear Ben et al.--I agree with the general practice of trying to estimate
and retain as many random effects as possible (without estimation issues)
in a mixed model. However, I was wondering whether anyone had some
references recommending or arguing for this approach. I am aware of a paper
on this topic with some simulation work by Barr et al. (2013; Journal of
Memory and Language), but I would be interested in whether there are
others. Thanks, J-P

Jean-Philippe Laurenceau, Ph.D.
Department of Psychological & Brain Sciences
University of Delaware


-----Original Message-----
From: R-sig-mixed-models [mailto:r-sig-mixed-models-bounces at r-project.org]
On Behalf Of Ben Bolker
Sent: Saturday, May 7, 2016 11:35 AM
To: Carlos Barboza <carlosambarboza at gmail.com>
Cc: r-sig-mixed-models at r-project.org
Subject: Re: [R-sig-ME] Comparing mixed models

  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-freed
om-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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