st: Interaction with squared variable

[Giuseppe Cappelletti <giuseppe.cappelletti@gmail.com>]

I would like to estimate an orderd probit model with the following
specification:

Prob(y=1) = x + a*gender + b*x + c*x^2 + d*gender*x^2

I tried the following command:

oprobit  y  ///
   i.gender   ///
   c.x   ///
   c.x#c.x  ///
   i.gender#(c.x#c.x)

but it does not work. After the estimation I would like to compute the
marginal effect (considering both the squared and interaction term).

Thanks in advance

Giuseppe

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/