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Re: st: margins / over / dydx
From
Richard Williams <[email protected]>
To
[email protected]
Subject
Re: st: margins / over / dydx
Date
Wed, 04 Jan 2012 13:09:10 -0500
At 04:19 AM 1/4/2012, Robert Duval wrote:
I can of course estimate
margins , over(sex) post
and then proceed "by hand" given that I have the parameter estimates
to differentiate and the variance-covariance matrix. However, I want
to do this for several models and for many different values in the
at() option. So before I program a complicated loop for my specific
problem in hand I wanted to ask if anyone knows a direct way of
obtaining the difference 0.2587496 - .0807707 = .1779789 and its
standard error.
Is the post option all that horrible? You could save and restore the
probit results if you want to do a bunch of different things with the
same model.
Does this do what you want? It at least saves you doing the
calculation by hand. You will need Stata 12 for this.
use http://www.stata-press.com/data/r11/margex
probit outcome sex##group age distance arm
margins, over(sex) post
contrast r.sex
The last command yields
. contrast r.sex
Contrasts of predictive margins
Model VCE : OIM
Expression : Pr(outcome), predict()
over : sex
------------------------------------------------
| df chi2 P>chi2
-------------+----------------------------------
sex | 1 218.99 0.0000
------------------------------------------------
--------------------------------------------------------------
| Delta-method
| Contrast Std. Err. [95% Conf. Interval]
-------------+------------------------------------------------
sex |
(1 vs 0) | .1779789 .012027 .1544063 .2015515
--------------------------------------------------------------
Also, note that contrast saves its results in r, e.g. after doing the above,
. mat list r(chi2)
symmetric r(chi2)[1,1]
c1
r1 218.98749
. mat list r(b)
symmetric r(b)[1,1]
r1vs0.
sex
r1 .17797889
. mat list r(V)
symmetric r(V)[1,1]
r1vs0.
sex
r1vs0.sex .00014465
. di .00014465^.5
.01202705
-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
HOME: (574)289-5227
EMAIL: [email protected]
WWW: http://www.nd.edu/~rwilliam
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