You would be better off posting to R-sig-mixed-models or R-sig-ecology -- Bert
On Thu, Nov 18, 2010 at 9:58 AM, Simon Garnier <sgarn...@princeton.edu> wrote: > Dear all, > > I'm discovering the somehow confusing (for me) world of linear mixed models > after having been advised it could be the best option to analyze my dataset. > After several days of reading, I'm not sure that what I ended up with makes > some sense and I'd greatly appreciate any help and explanations. > > The dataset has been obtained as follows. In 15 different locations, I > counted during 10 seconds the number of ants crossing a gap, before and after > destroying a bridge that ants had previously built over the gap. I then > waited for the ants to rebuild the bridge and repeated two more times the > counting and destroying process. Therefore, for each gap observed, I have 3 > replicates of the same experiment, each of them providing 1 count value for > each treatment tested (before and after bridge destruction), i.e. 6 values in > total per gap. I also measured for each gap its length. > > I now want to model the effect of the gap length (GapLength, continuous > variable), the treatment (Treatment, categorical variable) and the replicate > position (Replicate, categorical variable) on the number of ants crossing the > gap (AntCount, count variable). As far as I understand, the gap (Gap) can be > treated here as a random effect, the gap length, the treatment and the > replicate position as fixed effects. Moreover, the treatment variable is > nested in the replicate position variable that is also nested in the gap > variable. Finally, since I have count data, a poisson distribution should be > used for the model. With all this information in mind and some additional > information from various sources, I ended up with the following R code: > > lmer(AntCount ~ Treatment + GapLength + (Treatment | Gap / Replicate) + > (GapLength | Gap), data=dat, family=poisson(link=log)) > > The code runs fine and does not return any error. But of course this does not > mean the model was correctly designed. Am I right when I'm doing this or am I > (most likely) completely wrong? > > Thanks in advance for your help. > > Best, > Simon. > > -- > -------------------------------------------------------------------------------- > Dr. Simon Garnier > Department of Ecology & Evolutionary Biology > Princeton University > Guyot Hall > > e-mail: sgarn...@princeton.edu / simon.garn...@gmail.com > website: http://www.simongarnier.com > photoblog: http://www.simongarnier.org > -------------------------------------------------------------------------------- > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Bert Gunter Genentech Nonclinical Biostatistics ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
