R help - Sep 2003 - logistic regression for a data set with perfect separation

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
doesn't work, since the ML algorithm does not converge

1: Algorithm did not converge in: (if (is.empty.model(mt)) glm.fit.null else glm
.fit)(x = X, y = Y,
2: fitted probabilities numerically 0 or 1 occurred in: (if (is.empty.model(mt))
 glm.fit.null else glm.fit)(x = X, y = Y,

Many thanks for your help

Christoph
-- 
Christoph Lehmann <christoph.lehmann at gmx.ch>

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>

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>
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>