[Rd] Estimating overdispersion when using glm for count and binomial data

Ben Bolker bbolker at gmail.com
Thu Jun 25 17:25:37 CEST 2015

David Fletcher <dfletcher <at> maths.otago.ac.nz> writes:

> Dear All
> I recently proposed a simple modification to Wedderburn's 1974 estimate 
> of overdispersion for count and binomial data, which is used in glm for 
> the quasipoisson and quasibinomial families (see the reference below).


> The modification is very simple and would take at most a couple of 
> lines of code. The reference below gives details regarding its 
> asymptotic properties, as well as simulation results that illustrate the 
> benefits of using it for sparse data.

> D.J. Fletcher (2012) Estimating overdispersion when fitting a 
> generalized linear model to sparse data. Biometrika 99:230–237 
> (http://biomet.oxfordjournals.org/content/99/1/230.abstract?etoc)

  This looks really useful.  Base R is very conservative; despite the
fact that it would be much more easily adopted in base R, I think it
is much more likely to find a home in an add-on package such as aods3
or glm2 than in base R ...

    Ben Bolker


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