[R-sig-ME] Comparing mixed models

[John Fox]

Dear Carlos,

 From ?Anova:

"Warning

Be careful of type-III tests: For a traditional multifactor ANOVA model 
with interactions, for example, these tests will normally only be 
sensible when using contrasts that, for different terms, are orthogonal 
in the row-basis of the model, such as those produced by contr.sum, 
contr.poly, or contr.helmert, but not by the default contr.treatment. In 
a model that contains factors, numeric covariates, and interactions, 
main-effect tests for factors will be for differences over the origin. 
In contrast (pun intended), type-II tests are invariant with respect to 
(full-rank) contrast coding. If you don't understand this issue, then 
you probably shouldn't use Anova for type-III tests."

I hope this helps,
  John

-- 
John Fox, Professor Emeritus
McMaster University
Hamilton, Ontario, Canada
web: https://www.john-fox.ca/
--
On 2024-06-18 5:59 a.m., Carlos Barboza wrote:
> [You don't often get email from carlosambarboza using gmail.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> 
> Caution: External email.
> 
> 
> sorry, Anova type III function form car package in R
> 
> Em ter., 18 de jun. de 2024 às 06:59, Carlos Barboza <
> carlosambarboza using gmail.com> escreveu:
> 
>> Dear all,
>> why Anova type III function gives different results if I change the names
>> of a categorical factor? I suspect that is because contrast type but it's
>> something strange get different results using the same data.
>> thank you
>>
>> Em sáb., 7 de mai. de 2016 às 12:26, Carlos Barboza <
>> carlosambarboza using gmail.com> escreveu:
>>
>>> 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 using 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
>>>
>>>
>>>
>>>
>>
>> --
>> Universidade Federal do Rio de Janeiro (UFRJ)
>> Instituto de Biodiversidade e Sustentabilidade - NUPEM
>> Caixa Postal 119331, CEP 27910-970
>> Macaé, RJ, Brazil
>> https://www.macae.ufrj.br/nupem/
>> http://lattes.cnpq.br/3629226944950076
>> https://scholar.google.com.br/citations?user=p-PRvd4AAAAJ&hl=pt-BR
>> https://www.researchgate.net/profile/Carlos_Barboza3
>>
> 
> 
> --
> Universidade Federal do Rio de Janeiro (UFRJ)
> Instituto de Biodiversidade e Sustentabilidade - NUPEM
> Caixa Postal 119331, CEP 27910-970
> Macaé, RJ, Brazil
> https://www.macae.ufrj.br/nupem/
> http://lattes.cnpq.br/3629226944950076
> https://scholar.google.com.br/citations?user=p-PRvd4AAAAJ&hl=pt-BR
> https://www.researchgate.net/profile/Carlos_Barboza3
> 
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> 
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