st: ivregress with censored endogenous regressor

["Facchini Palma, Gabriel Alejandro" <Gabriel.Facchini@eui.eu>]

Dear listers, 

I have a question regarding the best way to do a regression when I have to instrument an independent variable that is actually endogenous and censored (obs values <0 coded as zero). 

The problem here is that the normal ivregress command would perform an OLS regression in the first stage and that's biased. 

Then I can do a 2sls manually, running first a Tobit model on my censored variable with the instrument Z, and then plugging  the predicted xhat into an OLS regression with my final continuous outcome variable Y. But then would the mechanism used to correct the se in a standard 2sls work, or there's something else to take into account in this case?

I've seen some posts where it has been recommended to use only uncensored observations. The problem with that is that the assumptions behind that being consistent are quite strong and there are efficiency losses.

In case it helps, in my case the Y var is weight at birth, the endogenous censored var is # of cigarettes the mother consumed daily during pregnancy, and the Z instrument is cigarette excise taxes changes.

thanks in advance, 

Gabriel

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