[Rd] aic in binomial models is often wrong (PR#796)

[ripley@stats.ox.ac.uk]

The following two models are the same:

data(esoph)
glm(cbind(ncases, ncontrols) ~ agegp + tobgp * alcgp, 
    data = esoph, family = binomial())
...
Degrees of Freedom: 87 Total (i.e. Null);  67 Residual
Null Deviance:      227.2 
Residual Deviance: 47.48        AIC: 237 

glm(ncases/(ncases+ncontrols) ~ agegp + tobgp * alcgp, 
    data = esoph, family = binomial(), weights=ncases+ncontrols)
...
Degrees of Freedom: 87 Total (i.e. Null);  67 Residual
Null Deviance:      227.2 
Residual Deviance: 47.48        AIC: 934.4 

The second AIC value is wrong: fixed in R-patched now.

You may think you only ever use the first form, but internally
R uses the second quite a bit.

-- 
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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