[R] glm binomial with zero proportions

[Prof Brian Ripley]

On Wed, 1 Mar 2006, Bill Shipley wrote:

> Hello.  I must fit a logistic regression to data in the form of
> proportions, but in which some of the proportions are zero.  I therefore
> cannot use the glm function with a binomial link since the link function
> is not defined for p=0 or 1.

It is a logistic link, not a 'binomial link'.  The fitted proportions 
cannot be zero (just 2*10^-16 which is exceedingly rare), but the observed 
ones can.  MASS4 p.190 has an example with observed proportion zero.

> What other solutions are available?  Any
> references to this specific problem (i.e. regression using proportions,
> of which some are zero) would be welcome.

Any good book on logistic regression.

> Thanks.
>
> Bill Shipley
>
> 	[[alternative HTML version deleted]]
> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html

Oh please do give up sending HTML mail.

-- 
Brian D. Ripley,                  ripley at 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 272866 (PA)
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