st: biprobit postestimation (marginal effects)

[Fabian Guy <fabolous.vs@gmail.com>]

Dear Stata-Experts,
I need your advice with a simple biprobit postestimation analysis. I
think the problem that I have could be solved in a straightforward
manner, but since I am not that familiar with Stata I would like to
make sure that I do not mess things up.

So, suppose I have a panel of i=1,...,I individuals and for each
individual I have observation over time t=1,...,T.
I estimate the following _pooled_ bivariate probit model:
(y1 = L.y2 X)
(y2 = L.y1 X)
where X = common regressors in both equations (continuous, no binary
variable included in this set). The estimation turns out that
estimating a two equation probit is important, since the correlation
parameter of the errors is significantly different from zero.

I would like to compute the following marginal effects:
a) Given X is at the mean of the sample, y2=0 (1), and L.y1=0 (1),
what is the increase/decrease in the probability of y1=1 if L.y2
increases from 0 to 1?
b) Given X_subset is at the mean, y2=0 (1), and L.y1=0 (1), what is
the increase/decrease in the probability of y1=1 if X_j increases by
one unit?
c) Given X is at the mean, L.y2 = 0 (1) y2=1 (0), and L.y1 = 0 (1),
what is the Prob. of y1=1?

For me it looks like that those marginal effects could be typically
requested using biprobit. Do I have to use margins or predict for
these calculations? Do I have to code this by my own or is there a
Stata command with some options (like predict/margins) that could
provide me a solution to those calculations?

A possible variation would be to set L. variables as well to their
average, however, I think it does not make much sense for dichotomous
variables.

I appreciate any advice very much.

Best,
Fabian
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/