[R-sig-ME] Comparing mixed models

Jean-Philippe Laurenceau jlaurenceau at psych.udel.edu
Wed May 11 04:52:24 CEST 2016

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>

> 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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