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# Re: st: Conditional marginal effects in heckprob

 From Maarten buis To statalist@hsphsun2.harvard.edu Subject Re: st: Conditional marginal effects in heckprob Date Mon, 23 Aug 2010 14:44:40 +0000 (GMT)

```--- On Mon, 23/8/10, Garrido, Melissa wrote:
> 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(*)

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
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
--------------------------

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```