I was not using a package to calculate QAIC. I will look into your suggestions, though. I thought it would be simple to ask glm to just fix the overdisperion at a particular value. Apparently it is not.
Thank you for all you help. Manuela -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Ben Bolker Sent: Thursday, October 07, 2010 12:04 PM To: r-h...@stat.math.ethz.ch Subject: Re: [R] How do I set the dispersion parameter in poisson glm? Huso, Manuela <manuela.huso <at> oregonstate.edu> writes: > > Thank you so much for your reply, Z. Of course, you are correct about > the overdispersion not affecting > parameter estimation. But my goal is comparison of several models > using QAIC and the dispersion > parameter enters the QAIC calculation. I suppose I could calculate > the QAIC of all models using my fixed > dispersion parameter, but I was hoping I could just set it in the > glm call and let the software calculate > QAIC appropriately for me. [snip] Which QAIC() function are you using? The ones in the MuMIn,AICcmodavg, and bbmle packages all have parameters that should allow you to set the dispersion parameter when you calculate QAIC. ______________________________________________ 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. ______________________________________________ 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.
