Hi, Also consider using the function supplied in the post:
https://stat.ethz.ch/pipermail/r-help/2005-March/066752.html for fitting negative binomial mixed effects models. Cheers, Anders. On Tue, 5 Apr 2005, Achim Zeileis wrote: > On Tue, 5 Apr 2005 11:20:37 -0600 [EMAIL PROTECTED] wrote: > > > Greetings R Users! > > > > I have a data set of count responses for which I have made repeated > > observations on the experimental units (stream reaches) over two air > > photo dates, hence the mixed effect. I have been using Dr. Jim > > Lindsey's GLMM function found in his"repeated" measures package with > > the "poisson" family. > > > > My problem though is that I don't think the poisson distribution is > > the right one to discribe my data which is overdispersed; the variance > > is greater than the mean. I have read that the "negative binomial" > > regression models can account for some of the differences among > > observations by adding in a error term that independent of the the > > covariates. > > glm.nb() from package MASS fits negative binomial GLMs. > > > I haven't yet come across a mixed effects model that can use the > > "negative binomial" distribution. > > For known theta, you can plug negative.binomial(theta) into glmmPQL() > for example. (Both functions are also available in MASS.) I'm not sure > whether there is also code available for unknown theta. > > > If any of you know of such a function - I will certainly look forward > > to hearing from you! Additionally, if any of you have insight on > > zero-inflated data, and testing for this, I'd be interested in your > > comments too. I'll post a summary of your responses to this list. > > Look at package zicounts for zero-inflated Poisson and NB models. For > these models, there is also code available at > http://pscl.stanford.edu/content.html > which also hosts code for hurdle models. > > hth, > Z > > > Best Regards, > > Nadele Flynn, M.Sc. candidate. > > University of Alberta > > > > ______________________________________________ > > R-help@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 > > > > ______________________________________________ > R-help@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 > ______________________________________________ R-help@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