There may be a good reason for this, but under R 2.5.1 (Windows XP, Suse
Linux)
> glm(c(0,.5)~1,quasi(link=logit))
Error: NA/NaN/Inf in foreign function call (arg 4)
whereas the same code works under R 2.1.1.
The problem (in 2.5.1) is a -Inf in the pseudodata `z' in glm.fit, as a
result of a `-Inf' in eta, which is in turn generated by `mustart <-
y' and
`logit(mustart)'. In 2.1.1 the line `mustart <- y + 0.1 * (y == 0)'
is
what avoids the problem.
A possible fix might be to set elements of `good' to FALSE for non-finite
`eta', for the first fit iteration only, of course. Is it worth fixing? I
found this after someone reported a problem with mgcv::gamm (which
calls MASS:glmmPQL which calls glm), which is why I'm not just supplying
my own mustart and getting on with it...
best,
Simon
>- Simon Wood, Mathematical Sciences, University of Bath, Bath BA2 7AY
>- +44 (0)1225 386603 www.maths.bath.ac.uk/~sw283/