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Re: st: x predicts failure perfectly?


From   Richard J Stoll <stoll@rice.edu>
To   Stata listserv <statalist@hsphsun2.harvard.edu>
Subject   Re: st: x predicts failure perfectly?
Date   Mon, 5 Apr 2004 14:10:07 -0500 (CDT)

On Mon, 5 Apr 2004, Petersen, Karen  wrote:

> I have run into a perplexing problem.  I am using logit to analyze an outcome
> variable (mid)
>
> logit mid illibdem1 limdyn1 absdyn1 auth1 pers1 cwpceyrs_werner rel_cap
> econ_dep1 econ_dep2 rel_energy allies if cat2_2==11 & exclude2==0 &
> initiate~=2, cluster(dyad_id)
>
> and get the following message about one of my explanatory variables (absdyn1):
>
> note: absdyn1 != 0 predicts failure perfectly
>       absdyn dropped and 68 obs not used
> Does anyone know why I get the above error message when the variable does not
> appear to actually be a "perfect predictor"?
>
I suspect that it is a perfect predictor in the logit because you are
losing cases due to misssing data on the other variables in the equation.
------------------------------------------------------------------------
Richard J. Stoll, Professor of Political Science and
Associate Dean of Social Sciences * Rice University
Dept. Political Science MS 24 * P.O. Box 1892 * Houston TX 77251-1892
E-mail: stoll@rice.edu * Tel: 713-348-3362 * FAX: 713-348-5273

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