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st: Heckman comand sample issue

From   Michael McQuestion <>
Subject   st: Heckman comand sample issue
Date   Wed, 21 Apr 2004 09:04:34 -0400

Nicholas Theopold,

I have also had the problem with the Heckman model you describe. Some of my
bright students pointed out that only the subset of observed outcomes are
used when there is an = sign in the selection equation:

heckman lb_tot_u mat_ed2 toilet2 pr_spoc1, sel (nomort= cdfocndx)mills(imru)

But all observations are used when we remove the = sign:

heckman lb_tot_u mat_ed2 toilet2 pr_spoc1, sel (nomort cdfocndx)mills(imru2)

I hope this helps.

Michael J. McQuestion
Assistant Professor
Johns Hopkins Bloomberg School of Public Health
Department of Population and Family Health Sciences
615 Wolfe Street, Rm. E-4142
Baltimore, MD  21205

phone (410) 502-6037
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