[R-sig-ME] glmm question

Lionel hughes.dupond at gmx.de
Wed Sep 2 23:08:36 CEST 2015

Dear Joaquin,

I did not look in your script but here are my thoughts on your question:
- concerning residuals, the choice of accepting a model as fitting to 
the data or not based on residuals plot (ie residuals vs fitted value) 
is at the discretion of the analyst/scientist. Sometime when I am unsure 
I simulate data from the model (ie simulate for merMod object), fit 
these simulated data to the model (ie function refit for merMod) and see 
if the resulting residual plot differ from the one I got from my 
empirical data. If yes my model is wrong, otherwise the model is not so bad.

- Two-way interaction between categorical variables or between a 
categorical and continuous variable are rather easy to understand, it 
gets trickier for interaction between two continuous variables, I wrote 
an article on this a while back: http://rpubs.com/hughes/15353, this was 
for lm but for glmm the interpretation would be the same (except that we 
have a link function, log in the case of poisson, between the observed 
data and the modeled response). There are certainly many more resource 
out there, I found the UCLA pages nicely written: 


On 02/09/2015 20:45, Joaquín Aldabe wrote:
> Hello, I sent this message but not sure if you received. I really
> appreciate any comment. Thanks a lot, Joaquín.
> 2015-09-01 17:58 GMT-03:00 Joaquín Aldabe <joaquin.aldabe at gmail.com>:
>> Hello, I´m trying to model de abundance of a grassland shorebird
>> (Buff-breasted Sandpiper, BBSA) as a function of the abundance of American
>> Golden Plover (AMGP) abundance, grass height and distance to the lagoon.
>> I´m using area as an offset.
>> I´ve tried a glmm with poisson errors and wanted you to see if residuals
>> are fine (they don´t look great, but wanted to know if they area minimally
>> acceptable). Also, I´m trying to understand two way interactions but I´m no
>> sure how to proceed, and also would like to plot the interactions and
>> unique variables effects (can you please provide suggestions?).
>> I also have problems with the predict function. In the script are the
>> notes. I´m attaching the data as well as the script with commentaries.
>> Let me know if there´s some format problem with the files.
>> Thank you very much in advanced.
>> Joaquín.
>> --
>> *Joaquín Aldabe*
>> *Grupo Biodiversidad, Ambiente y Sociedad*
>> Centro Universitario de la Región Este, Universidad de la República
>> Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha
>> *Departamento de Conservación*
>> Aves Uruguay
>> BirdLife International
>> Canelones 1164, Montevideo
>> https://sites.google.com/site/joaquin.aldabe
>> <https://sites.google.com/site/perfilprofesionaljoaquinaldabe>

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