[R] Comparing negative binomial models

Ben Bolker bbolker at gmail.com
Thu Nov 3 20:55:17 CET 2011

Davg <davidgrimsey <at> hotmail.com> writes:

> I am trying to compare negative binomial models for the prediction of sports
> games (I know that Poisson models would be better but I'm just trying
> Negative Binomial at the moment).
> But, to compare the models I need them to have the same theta value.  How
> can I change the explanatory variables while maintaining the theta value?

  modelfit <- glm(..., family=negative.binomial(theta=theta_value))

I believe that drop1() applied to a glm.nb() fit does this correctly
(i.e. holds the theta parameter fixed at the estimate from the most complex

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