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Re: st: Missing standard error and confidence intervall for a dummy

From   Maarten buis <>
Subject   Re: st: Missing standard error and confidence intervall for a dummy
Date   Fri, 10 Aug 2007 11:57:41 +0100 (BST)

--- georg wernicke <> wrote:
> I have used a heckman twostep selection process. After employing the
> test I get 2 tables, the selection and the regression table. What
> puzzles me, that in the one of the tables STATA gives me the
> coefficient but does not report a standard error, confidence
> intervall and the z value for a dummy but does so in the other 
> regression table.

One possibility is that the dummy is a nearly perfectly predictor in
the selection equation. The way to find that out is to look at a table
of the selection variable against the dummy. You can do that as

gen select = !missing(y)
tab select baddummy

(Assuming that your dependent variable is called y and the bad dummy is
called baddummy) 
Hope this helps,

Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

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