The Gravity Model and the Problem of Zero`s in Agrifood Trade

and this is a problem when estimating log-linear gravity equations. This has caused many researchers to either ignore the zero trade flows or to replace the zero with a small positive number. Both of these actions bias the resulting parameter estimates of the gravity equation. In this study we correct for this misspecification by using the Heckman selection model to estimate bilateral trade flows for 46 agrifood products, for the period 1990 to 2000, for 52 countries. In our sample, selection bias rarely affects the signs of variables but often has a substantial effect on the magnitude, statistical significance and economic interpretation of the marginal effects. Hence, treating zero trade flows properly is important from both a statistical and an economics perspective.


Issue Date:
2011-08
Publication Type:
Working or Discussion Paper
PURL Identifier:
http://purl.umn.edu/116851
Total Pages:
28
Series Statement:
Working Paper
WP 2011-02




 Record created 2017-04-01, last modified 2017-04-04

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