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Re: st: problem with heckman procedure


From   "Brian P. Poi" <bpoi@stata.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: problem with heckman procedure
Date   Tue, 25 Sep 2007 10:10:25 -0500 (CDT)

On Tue, 25 Sep 2007, Zeenat Soobedar <z.soobedar@qmul.ac.uk> wrote:

I am doing the heckman procedure using a loop because I need to do it for several years But when STATA executes the command which is as follows:

xi: heckman wf i.agegroup i.qual, twostep select(i.agegroup i.qual
i.agegroup*i.qual ym) mills(mills`y')

/* `y' stands for 1980 1990 2000 */

the program stops and I get the following error: matrix has missing values
r(504);

So I drop the mills ratio generated and then rerun the same command and
then it works. But the thing is that I have to run this one line command
on its own.

Without seeing the dataset, it's hard to tell what is causing this error message. Zeenat, if you send your dataset to me privately (bpoi@stata.com), I'd be happy to look into the problem for you.

-- Brian Poi
-- bpoi@stata.com


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