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# RE: st: Conditional marginal effects in heckprob

 From "Garrido, Melissa" To Subject RE: st: Conditional marginal effects in heckprob Date Mon, 23 Aug 2010 12:59:29 -0400

```
Thank you, Maarten; that helped a lot.

Melissa
________________________
I assume that with conditional marginal effects you
mean the marginal effect on the predicted probability
of success conditional on selection. In that case
you need to add the -predict(pcond)- option. Right
now, you are estimating the marginal effect on
probability of success.

The -predict()- option in -margins- determines what
your response/dependent/explained/y variable is, and
if you do not specify it, it will assume that it is
the default for -predict-. If you look at
-help heckprob postestimation-, you will see that the
default is -pmargin-, which is described as

"the default, calculates the univariate (marginal)
predicted probability of success; Pr(depvar=1)"

You probably want:

"pcond calculates the conditional (on selection)
predicted probability of success; Pr(depvar=1 |
depvar_s=1) = Pr(depvar=1, depvar_s=1)/Pr(depvar_s=1)."

Hope this helps,
Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------

-----Original Message-----
From: Garrido, Melissa
Sent: Monday, August 23, 2010 10:14 AM
To: 'statalist@hsphsun2.harvard.edu'
Subject: Conditional marginal effects in heckprob

Hi -

I have a question about the -margins- command in Stata 11, when used
after heckprob.

I want to get conditional marginal effects of my outcome variable, but
I'm not sure whether I have the correct syntax (and haven't found the
answer in the help files).

Is the default option within -margins- to calculate the conditional
marginal effect, or is there something additional I need to specify?

Here is what I have:

****

heckprob diedvsroutinetotal = \$indepvar , select (not_transfer =
\$indepvar \$instruments)

/*Marginal effects at means:*/

margins, dydx(*) atmeans

/*Average marginal effect:*/

margins, dydx(*)

***

Thank you,

Melissa

--------------------------------------------------------------------
Melissa Garrido, PhD

Research Health Science Specialist
GRECC/REAP, James J Peters VA Medical Center
130 West Kingsbridge Road
Bronx, NY 10468
718-584-9000 x 3804
melissa.garrido@va.gov

Assistant Professor
Department of Geriatrics & Palliative Medicine
Box 1070
Mount Sinai School of Medicine
One Gustave L. Levy Place
New York, NY 10029
melissa.garrido@mssm.edu

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