[R] Assessing overdispersion and using quasi model with lmer, possible?

swertie v_coudrain at voila.fr
Thu Oct 18 16:23:47 CEST 2012

I am trying to model data on species abundance (count data) with a poisson
error distribution. I have a fixed and a random variables and thus needs a
mixed model. I strongly doubt that my model is overdispersed but I don't
know how to get the overdispersion parameter in a mixed model. Maybe someone
can help me on this point. Secondly, it seems that quasi models cannot be
implemented with the function lmer, is there an option? If not, I certainly
should go to variable transformation and use a gaussian error distribution,
but it is not optimal.
Thank you!

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