[R] glm binomial with zero proportions
Prof Brian Ripley
ripley at stats.ox.ac.uk
Wed Mar 1 16:16:21 CET 2006
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.
> 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)
Oxford OX1 3TG, UK Fax: +44 1865 272595
More information about the R-help