Hello,

I am a PhD student currently trying to derive a mixed effects model.

I would like to describe the relationship between age and male 
reproductive success in a population of greater horseshoe bats.

My data consists of three columns: MaleID, Age, NumberofPups (at that 
age). Many of the males appear multiple times in the data set, so I 
believe I need to derive a mixed model with MaleID as a random variable.

The data is Poisson distributed, but zero-truncated. So far I have only 
succeeded in making a mixed model with a poisson distribution (using 
glmmPQL in the MASS package), and a zero truncated poisson model (using 
vglm in the VGAM package), but not a mixed model capable of handling 
zero truncated Poisson data.

It has been suggested that I could just minus 1 from each value in the 
NumberofPups column to make a more usual Poisson distribution, so I can 
ignore the zero truncated bit. I have tried this and it changes the 
results of the model, but is this an acceptable transformation?

If not, can anyone advise me on a mixed model that can handle zero 
truncated Poisson data please?

I also intend to post this on the R-sig-mixed-models 
<https://stat.ethz.ch/mailman/options/r-sig-mixed-models/h.l.ward%40qmul.ac.uk> 
list, so apologies if you've seen it twice!

Many thanks,
Helen


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