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st: Heckprob error: outcome = y_select > 0 predicts data perfectly


From   Dave Francis <dafrancis11@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Heckprob error: outcome = y_select > 0 predicts data perfectly
Date   Thu, 27 Jan 2011 11:58:52 -0800 (PST)

Hi, 

I am trying to a heckprob model on the disappearance of firms. Basically, I have 
a selection equation where firms are coded 0 if they existed in the first stage 
of my panel but not the second statge. The firms are coded 1 if they are in 
existence in both periods of the panel. Secondly, I have a binary outcome stage 
equation, which is equal to 1 if a firm answers a specific question; 0 if it 
does not. 


I'm getting this error: outcome = y_select > 0 predicts data perfectly, where 
y_select is the dependent variable for my selection equation. Thoughts? Clearly 
since firms that are not "selected" are those that are no longer in existence, 
they cannot answer and so they are coded as missing for y_outcome, the DV of the 
outcome equation.

Thoughts?

Many thanks

Here is a tab of the two y_* vars

. tab y_outcome y_select, m
                |         y_select
y_outcome  |   0          1 |     Total
-----------+----------------------+----------
         0 |         0         95 |        95 
         1 |         0        178 |       178 
         . |        70          0 |        70 
-----------+----------------------+----------
     Total |        70        273 |       343 


      

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