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st: AW: Tobit, negative predictesd values

From   "Martin Weiss" <>
To   <>
Subject   st: AW: Tobit, negative predictesd values
Date   Tue, 10 Nov 2009 13:52:32 +0100


" a published paper by Zwick in 2002(Centre for European Economic Research)"

You are probably referring to ?
Note the onus is on you to provide the reference...


-----Ursprüngliche Nachricht-----
[] Im Auftrag von Solorzano
Mosquera, Jenniffer
Gesendet: Montag, 9. November 2009 23:59
An: ''
Betreff: st: Tobit, negative predictesd values

Hi everyone,
I estimated a tobit model having intensity labor training as dependent
variable and a group of firm characteristics which are presumpted as
determinants of that intensity. I need to predict the estimated intensity to
use it in a second stage model to know what is the impact in firm
productivity. I'm using the whole sample, those firms offering training and
those who are not. I'm censoring to the interval 0,1. However I obtain
negative predicted variables from the tobit.

I have 0's for those firms who decided not to offer training, following a
published paper by Zwick in 2002(Centre for European Economic Research).
That way allows not to lose observations from the firms who have missing
values in the intensity variable because they decided not to offer training.
However I've been looking and I found that heavy censoring causes these kind
of problems on predicted values and even worse when high proportion of
censored cases is the situation.

Any suggestion to obtain tobit predicted values non-negatives or is it can
be interpreted as a expected result?


Jenniffer Solorzano Mosquera
Labor Markets Division - Inter-American Development Bank
Washington, DC - USA
(202) 623-3659

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