Dispersion parameter calculation for Poisson glmer

Hi All,

I would like to calculate a dispersion parameter for a glmer with a  
Poisson family (in lme4). I found a function posted on this mailing  
list that had been suggested to use for calculating a dispersion  
parameter for a glmer with a binomial family. (Found on   
https://stat.ethz.ch/pipermail/r-sig-mixed-models/2011q1/015383.html )

dispersion_glmer <- function(modelglmer)
	{n <- length(modelglmer at resid)
	return(sqrt( sum(c(modelglmer at resid, modelglmer at u)^2)/n))
	}

Am I allowed to use this for a Poisson glmer as well?

Thanks a bunch,

Justin Baldwin