extracting dispersion parameter from quasipoisson lmer model

Hi,
  I would like to obtain the dispersion parameter for a quasipoisson model
for later use in calculating QAIC values for model comparison.Can anyone
suggest a method of how to go about doing this?
   
  The idea I have now is that I could use the residual deviance divided by
the residual degrees of freedom to obtain the dispersion parameter. The
residual deviance is available in the summary output for the lmer model.
The problem with this idea is that the residual degrees of freedom is not
directly available. I have been assuming that the estimated/approximate DF
can be obtained through the formula listed below, and then subsequently
used to obtain the dispersion parameter as described above. Is this
correct?
   
  samp.m4 <- mcmcsamp(m4, n = 1000)
print(summary(samp.m4))
(eDF <- mean(samp.m4[,"deviance"]) - deviance(m4, REML=FALSE)) 
  # potentially useful approximate DF?

   
  However, rather than going through this roundabout, there appears to be
an easier way to obtain the dispersion parameter. I have noted that the
'quasibinomial' produces a dispersion parameter in the model output, but
the 'quasipoisson' output does not contain this useful number. Given that
each of my models is fit by lmer with a quasipoisson distribution, the
program must be internally calculating the dispersion parameter as it
runs. Perhaps there is a way to obtain this number directly since I assume
it has already been calculated? Can somone who has experience with this
code provide some advice on whether this is possible and how I might
manage to do this?
   
   
  Thank you for your time,
   
  Wayne Hallstrom
  403-370-3832
   
   

       
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