glmm question
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: http://www.ats.ucla.edu/stat/r/ Yours, Lionel
On 02/09/2015 20:45, Joaqu?n Aldabe wrote:
Hello, I sent this message but not sure if you received. I really appreciate any comment. Thanks a lot, Joaqu?n. 2015-09-01 17:58 GMT-03:00 Joaqu?n 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. Joaqu?n. -- *Joaqu?n Aldabe* *Grupo Biodiversidad, Ambiente y Sociedad* Centro Universitario de la Regi?n Este, Universidad de la Rep?blica Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha *Departamento de Conservaci?n* Aves Uruguay BirdLife International Canelones 1164, Montevideo https://sites.google.com/site/joaquin.aldabe <https://sites.google.com/site/perfilprofesionaljoaquinaldabe>