[Rd] BIC doesn't work for glm(family=binomial()) (PR#8208)

[Peter Dalgaard]

jusung at andrew.cmu.edu writes:

> Full_Name: Ju-Sung Lee
> Version: 2.2.0
> OS: Windows XP
> Submission from: (NULL) (66.93.61.221)
> 
> 
> BIC() requires the attribute $nobs from the logLik object but the logLik of a
> glm(formula,family=binomial()) object does not include $nobs.  Adding
> attr(obj,'nobs') = value, seems to allow BIC() to work.
> 
> Reproducing the problem:
> library(nmle);
> BIC(logLik(glm(1~1,family=binomial())));

It is not clear to me that "nobs" is a well-defined concept for
arbitrary likelihood functions. In particular, binomial models are
tricky: Is "13 successes in 79 trials" one (binomial) observation or
79 (Bernoulli) ones?? 

So BIC may not be defined. In which sense is this a bug, anyway? The
BIC function is defined inside the nlme package which is not designed
to work with anything but continuous data.


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