[R] not R question : alternative to logistic regression
Ben Bolker
bolker at ufl.edu
Thu Nov 15 21:25:45 CET 2007
MARK LEEDS-3 wrote:
>
> I was just curious if anyone knew of an alternative model to logistic
> regression where the probabilities seems pretty linear to the predictor
> rather than having that S shape that probit and logit assume.
>
>
Well, the logistic curve is very close to linear over the middle range of
probabilities --
are your probabilities all in the middle, or do they seem to hit 0 and 1
fairly sharply?
Using the formula interface to mle in the bbmle package (blatant plug),
you
could do something like
mle2(surv~dbinom(prob=pmin(pmax(a+b*x,0.001),0.999),size=1),start=...)
the pmin/pmax cut the probabilities off before they get to 1 or 0.
I'm not sure this is a good idea, but it is possible.
cheers
Ben Bolker
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