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

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  • Haq, Zahoor Ul
  • Meilke, Karl D.
  • Cranfield, John A.L.

Abstract

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.

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Bibliographic Info

Paper provided by Canadian Agricultural Trade Policy Research Network in its series Working Papers with number 116851.

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Date of creation: Aug 2011
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Handle: RePEc:ags:catpwp:116851

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Related research

Keywords: Gravity model; selection bias; Agrifood Trade; Heckman Selection Model; marginal effects; Agricultural and Food Policy; Demand and Price Analysis; International Relations/Trade; Research Methods/ Statistical Methods;

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  1. Haq, Zahoor Ul & Meilke, Karl D. & Cranfield, John A.L., 2010. "Does the Gravity Model Suffer from Selection Bias?," Working Papers 90884, Canadian Agricultural Trade Policy Research Network.
  2. Sampath Jayasinghe & John C. Beghin & GianCarlo Moschini, 2009. "Determinants of World Demand for U.S. Corn Seeds: The Role of Trade Costs," Center for Agricultural and Rural Development (CARD) Publications 09-wp484, Center for Agricultural and Rural Development (CARD) at Iowa State University.
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  11. Russell H. Hillberry, 2002. "Aggregation bias, compositional change, and the border effect," Canadian Journal of Economics, Canadian Economics Association, vol. 35(3), pages 517-530, August.
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  13. Baier, Scott L. & Bergstrand, Jeffrey H., 2009. "Bonus vetus OLS: A simple method for approximating international trade-cost effects using the gravity equation," Journal of International Economics, Elsevier, vol. 77(1), pages 77-85, February.
  14. Carmen Fillat-Castejon & Jose Ma Serrano-sanz, 2004. "Linder Revisited: Trade and Development in the Spanish Economy," International Review of Applied Economics, Taylor & Francis Journals, vol. 18(3), pages 323-348.
  15. Baier, Scott L. & Bergstrand, Jeffrey H., 2001. "The growth of world trade: tariffs, transport costs, and income similarity," Journal of International Economics, Elsevier, vol. 53(1), pages 1-27, February.
  16. Ga�l Raballand, 2003. "Determinants of the Negative Impact of Being Landlocked on Trade: An Empirical Investigation Through the Central Asian Case," Comparative Economic Studies, Palgrave Macmillan, vol. 45(4), pages 520-536, December.
  17. Bruno Henry de Frahan & Mark Vancauteren, 2006. "Harmonisation of food regulations and trade in the Single Market: evidence from disaggregated data," European Review of Agricultural Economics, Foundation for the European Review of Agricultural Economics, vol. 33(3), pages 337-360, September.
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