st: conditional probabilities after biprobit

[george joseph <gjosephresearch@gmail.com>]

after biprobit.

 I have the following code

 biprobit (y1 = y2 xvars) (y2 z xvariables ), robust

 After mfx, compute, I try to calculate the conditional probability
of-  y1=1 conditional on y2=1 and then  y1=1 conditional on y2=0. I
found > the following faq on the stata list useful.

http://www.stata.com/statalist/archive/2010-/msg00078.html
 The following suggestion is provided. However, I am not sure whether
this calcualation is indeed correctt, because it does not take into
consideration the complementary events. Also when we make all x equal
to 1 and then all x equal to 0, what exactly are we trying to do here.




 sysuse nlsw88, clear
 g x=race==1
 g y=married
 biprobit (y=x grade south smsa) (x=industry occupation union)
 mfx
 margins, dydx(*)
 g wasx=x
 replace x=1
 predict p1a, p11
 predict p1b, p10
 predict p1c, p01
 predict p1d, p00
 g p1=p1a/(p1a+p1c)
 replace x=0
 predict p0a, p11
 predict p0b, p10
 predict p0c, p01
 predict p0d, p00
 g p0=p0b/(p0b+p0d)
 replace x=wasx
 drop wasx
 g dp=p1-p0
 su dp

 Could anyone in the list clarify thiss

 Thanks.
 George

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