st: difference between -heckman- and -treatreg-

[Shehzad Ali <sia500@york.ac.uk>]

Hi,

I was wondering if someone can explain the difference between how -heckman- 
and -treatreg are estimated. I understand that analysts usually prefer 
-heckman- for sample selection bias and -treatreg- for endogeneity bias. 
But I was not sure how the two models are different computationally because 
they both use hazard ratio (or inverse Mills). Is hazard ratio different 
from IMR? Can anyone direct me to an article that explains the 
computational and theoretical difference between the two models?

Thank you,

Shehzad
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