[R] How do I set the dispersion parameter in poisson glm?

[Huso, Manuela]

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-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Ben Bolker
Sent: Thursday, October 07, 2010 12:04 PM
To: r-help at 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.

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