st: Heckman Selection Rule

[mtavoni <mtavoni@Princeton.EDU>]

Dear all,

a quick question on sample selection estimation. In Heckman, STATA 
estimates the parameters in the model:

       (regression equation: y is depvar, x is varlist)
       y = xb + u_1

       (selection equation: Z is varlist_s)
       y observed if Zg + u_2 > 0


What if I want to change the rule for the selection equation to something like: 

 y observed if Zg + u_2 < Constant


thanks for helping out.

cheers
max

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