[Rd] How do I know if the deviance of a glm fit was fixed?

Thomas Lumley tlumley@u.washington.edu
Fri, 18 Jan 2002 09:14:54 -0800 (PST)

On Fri, 18 Jan 2002, Duncan Murdoch wrote:

> I'm writing functions that need to behave differently for
> GLMs like binomial and Poisson with fixed deviance, and those like
> normal or gamma or quasi where the deviance is estimated from the
> data.  Given a glm object, is there a simple way to tell this
> directly, or do I have to look at the name of the family?

I assume you  mean dispersion rather than deviance.

You have to look.  This information can be specificied by the user to
summary.glm(), but not to glm() itself. Presumably the reason is that the
fit doesn't depend on the dispersion.


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