Re: [R] AIC for quasipoisson link

From: Marc Schwartz <>
Date: Fri, 31 Oct 2008 14:29:45 -0500

on 10/31/2008 01:07 PM wrote:
> Dear fellows,
> I'm trying to extract the AIC statistic from a GLM model with quasipoisson link.
> The formula I'm referring to is
> AIC = -2(maximum loglik) + 2df * phi
> with phi the overdispersion parameter, as reported in:
> Peng et al., Model choice in time series studies os air pollution and mortality. J R Stat Soc A, 2006; 162: pag 190.

> Unfortunately, the function logLik doesn't work for a quasipoisson link.
> Do you know a fast method to extract the AIC for these models?
> Thanks in advance

I was under the impression that there is no log likelihood for quasi* family models, thus no AIC, which is why they are not calculated/printed in the glm() summary outputs.

If you want to model overdispersed data and need the AIC, you should look at glm.nb() in MASS for a negative binomial model:


This would also avail you of the anova.glm() methods for comparing models, which the quasi* families would not.

You might also want to look at:

which is the vignette from the pscl package.

HTH, Marc Schwartz mailing list PLEASE do read the posting guide and provide commented, minimal, self-contained, reproducible code. Received on Fri 31 Oct 2008 - 19:33:01 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Fri 31 Oct 2008 - 20:30:21 GMT.

Mailing list information is available at Please read the posting guide before posting to the list.

list of date sections of archive