Stata The Stata listserver
[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

st: Regressor with too many zeros

From   "joe jacob" <>
Subject   st: Regressor with too many zeros
Date   Thu, 18 Sep 2003 05:36:44 +0000

Dear all,

I am estimating the effect of export orientation (exports/sales) by firms on their learning efforts from imported inputs. I use an -ivtobit- model due to the censored natured of the learning variable and the endogenous nature of the export intensity variable. There are a few other explanatory variables also, which capture the level of skill and technological capability of the firm. The problem is that there are a large number of non-exporting firms (hence a zero value for many observations of the export intensity variable). My estimation did not produce a significant positive relation between export intensity and learning. BUT when I added an export dummy (1 for exporters and 0 for non-exporters) the variable became highly significant. (both export intensity and export dummy were instrumented) However, the export dummy became significant Negatively with a higher coefficient value. This latter result seems very counter-intuitive.

Put simply, the question is thus, when the key regressor has too many zeros (as my export intensity variable has), how do we tackle the problem of non-variability? Simply excluding zero-valued observations don't seem right?

Please comment.



The hottest things. The coolest deals. Get them online!

* For searches and help try:

© Copyright 1996–2022 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index