Hello, I have the exact same question: how to extract dispersion parameter from lmer() quasipoisson model?
I did a search here and saw this post. However, I do not see answer. Could somebody please help? Thank you very much, Julia wayne hallstrom wrote: > > 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 > > > > > --------------------------------- > > [[alternative HTML version deleted]] > > ______________________________________________ > r-h...@stat.math.ethz.ch 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. > > -- View this message in context: http://www.nabble.com/extracting-dispersion-parameter-from-quasipoisson-lmer-model-tp11992221p22441798.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.