*
* TOBIT.RPF
* RATS Version 8, User's Guide, Example 12.3.
* From Verbeek(2008), Guide to Modern Econometrics, example 7.4.3
*
open data tobacco.asc
data(format=free,org=columns) 1 2724 bluecol whitecol flanders  $
  walloon nkids nkids2 nadults lnx share2 $
  share1 nadlnx agelnx age d1 d2 w1 w2 lnx2 age2
*
* Tobit I models
*
ldv(lower=0.0,censor=lower) share1
# constant age nadults nkids nkids2 lnx agelnx nadlnx
ldv(lower=0.0,censor=lower) share2
# constant age nadults nkids nkids2 lnx agelnx nadlnx
*
* OLS regressions on positive observations only
*
linreg(smpl=share1>0) share1
# constant age nadults nkids nkids2 lnx agelnx nadlnx
linreg(smpl=share2>0) share2
# constant age nadults nkids nkids2 lnx agelnx nadlnx
*
* Tobit II models, which require first step probits for non-zero
* consumption. While not strictly necessary, we remap the share values
* into 0-1 dummies. (DDV would work fine with just the zero-non-zero
* coding).
*
set choice1 = share1>0
set choice2 = share2>0

ddv(noprint) choice1
# constant age nadults nkids nkids2 lnx $
    agelnx nadlnx bluecol whitecol
prj(mills=lambda)
linreg(smpl=share1>0,title="Tobit II") share1
# constant age nadults nkids nkids2 lnx agelnx nadlnx lambda
*
ddv(noprint) choice2
# constant age nadults nkids nkids2 lnx $
    agelnx nadlnx bluecol whitecol
prj(mills=lambda)
linreg(smpl=share2>0,title="Tobit II") share2
# constant age nadults nkids nkids2 lnx agelnx nadlnx lambda