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st: Truncated sample or Heckman selection


From   Ebru Ozturk <ebru_0512@hotmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Truncated sample or Heckman selection
Date   Wed, 3 Oct 2012 12:41:16 +0300

Dear All,

I have a question that I cannot decide whether I should use truncated regression or Heckman sample selection. 

For instance, in the dataset, firms that produce any type of innovation (process or product) give information about other 'x' variables. In other words, firms that do not produce any innovation do not answer other questions as these questions are directly related to firms' innovation activities. So, the 'x' variables that I am interested in have no values only for those firms that do not produce innovation. But, I know the dependent (y) variable in both case, either firms produce innovation or not produce.

I am planning to run tobit regression as the dependent variable is percentage between 0 - 100 and Heckman sample selection model to check selection bias. But, I can not decide whether it is truncated sample or Heckman sample selection.
 
So, what do you think?
 
Thank you very much, Ebru.
  		 	   		  
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