[R] logistic regression for a data set with perfect separation

[Juan Carlos Correa Morales]

Hi:
Look at

Rousseeuw, P. J. and Christmann, A. (2003) Robustness against separations
and outliers in logistic regression, Computational Statistics & Data
Analysis, Vol. 43, pp. 315-332

Juan Carlos Correa, Ph.D.
Escuela de Estadistica
Universidad Nacional- Sede Medellin
Medellin COLOMBIA


On Wed, 10 Sep 2003, Christoph Lehmann wrote:

> Dear R experts
>
> I have the follwoing data
>           V1 V2
> 1 -5.8000000  0
> 2 -4.8000000  0
> 3 -2.8666667  0
> 4 -0.8666667  0
> 5 -0.7333333  0
> 6 -1.6666667  0
> 7 -0.1333333  1
> 8  1.2000000  1
> 9  1.3333333  1
>
> and I want to know, whether V1 can predict V2: of course it can, since
> there is a perfect separation between cases 1..6 and 7..9
>
> How can I test, whether this conclusion (being able to assign an
> observation i to class j, only knowing its value on Variable V1)  holds
> also for the population, our data were drawn from?
>
> Means, which inference procedure is recommended? Logistic regression,
> for obvious reasons makes no sense.
>
> Many thanks for your help
>
> Christoph
> --
> Christoph Lehmann <christoph.lehmann at gmx.ch>
>
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