[R] Estimating theta for negative binomial model

Prof Brian Ripley ripley at stats.ox.ac.uk
Tue May 4 07:50:42 CEST 2010

On Mon, 3 May 2010, Tim Clark wrote:

> Dear List,
> I am trying to do model averaging for a negative binomial model 
> using the package AICcmodavg.  I need to use glm() since the package 
> does not accept glm.nb() models.  I can get glm() to work if I first 
> run glm.nb and take theta from that model, but is there a simpler 
> way to estimate theta for the glm model?  The two models are:
> mod.nb<-glm.nb(mantas~site,data=mydata)
> mod.glm<-glm(mantas~site,data=mydata, family=negative.binomial(mod.nb$theta))
> How else can I get theta for the family=negative.binomial(theta=???)

library(MASS) is missing here -- do give credit where credit is due.
It contains functions


and the first does what you seem to want and the second answers the 
actual question you asked.

> Thanks!
> Tim
> Tim Clark
> Department of Zoology
> University of Hawaii

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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