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

Prof Brian Ripley ripley@stats.ox.ac.uk
Fri, 18 Jan 2002 17:26:01 +0000 (GMT)

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?

Did you mean dispersion fixed?

S/R do not take the dispersion into account: it is not in the fit.
It is used by the summary, predict and anova methods (and that's all as I
recall).  And they do look at the family name.

Brian D. Ripley,                  ripley@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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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