Dear statalisters, I am trying to estimate a generalized tobit model with two steps. The first step is a probit equation which determines whether a firm undertakes R&D or not.
HTML Code:
 y1*=x1*b1 +u1
where
y1* is a latent variable and the firm undertakes research if y1*>0.
The second step is a tobit equation which determines the intensity of research if the firm actually does invest in R&D.
HTML Code:
 y2*=x2*b2 +u2
where
HTML Code:
 y2*=y2  (y2=actual observed research intensity) if y1*>0.
The errors u1 and u2 are correlated (jointly normally distributed). Then my question please is: 1)Is there a program/command which allows me to estimate the above steps/equations and the covariance matrix in a simple way? I am using Stata 15 Any suggestion and help is extremely welcome. Thank you very much.