st: Using a Tobit regression with the Heckman correction

["J. Boreham" <jb648@cam.ac.uk>]

Dear Statalist,

I'm very new to Stata, so apologise if this is a silly question. I'm 
looking to run a Tobit regression using the Heckman correction. My Heckman 
code is:

***** heckman fee age agesq curr_app curr_goal_d curr_goal_m curr_goal_f, 
/// select(transferred = age agesq curr_app curr_goal_d curr_goal_m 
curr_goal_f prom) twostep *****

But this uses OLS rather than a Tobit model. I instead attempted to create 
the two stage Heckman correction by first manually producing the inverse 
Mills ratio, and then running a Tobit regression:

***** probit transferred age agesq curr_app curr_goal_d curr_goal_m 
curr_goal_f prom

predict predicted_values, xb

generate denominator = normal(predicted_values)
generate numerator = normalden(predicted_values)
generate mills_ratio = numerator/denominator

tobit fee age agesq curr_app curr_goal_d curr_goal_m curr_goal_f mills_ratio
*****

However, this will not account for the non-standard errors one needs when 
using the Heckman correction.

So is it possible either to tell Stata to use a Tobit regression with the 
"heckman" command, or instead to get the correct standard errors when 
manually doing the correction by inserting the inverse Mills ratio?


Thanks for your consideration,

John Boreham
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