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

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

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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File URL: http://purl.umn.edu/116851
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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
Contact details of provider: Web page: http://www.catrade.org/

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  1. Wang, Z.K. & Winters, L.A., 1992. "The Trading Potential of Eastern Europe," Discussion Papers 92-21, Department of Economics, University of Birmingham.
  2. Jayasinghe, Sampath J.D.Y. & Beghin, John C. & Moschini, GianCarlo, 2010. "Determinants of World Demand for U.S. Corn Seeds: The Role of Trade Costs," Staff General Research Papers 31493, Iowa State University, Department of Economics.
  3. Muhammed Dalgin & Devashish Mitra & Vitor Trindade, 2004. "Inequality, Nonhomothetic Preferences, and Trade: A Gravity Approach," NBER Working Papers 10800, National Bureau of Economic Research, Inc.
  4. 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.
  5. 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.
  6. 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.
  7. Elhanan Helpman & Marc Melitz & Yona Rubinstein, 2007. "Estimating Trade Flows: Trading Partners and Trading Volumes," NBER Working Papers 12927, National Bureau of Economic Research, Inc.
  8. Peter Egger, . "An Econometric View on the Estimation of Gravity Models and the Calculation of Trade Potentials," WIFO Working Papers 141, WIFO.
  9. Joao Santos Silva & Silvana Tenreyro, 2005. "The log of gravity," LSE Research Online Documents on Economics 3744, London School of Economics and Political Science, LSE Library.
  10. 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.
  11. Anne-Célia Disdier & Stéphan Marette, 2010. "The Combination of Gravity and Welfare Approaches for Evaluating Nontariff Measures," American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 92(3), pages 713-726.
  12. 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.
  13. Peter Egger & Michael Pfaffermayr, 2003. "The proper panel econometric specification of the gravity equation: A three-way model with bilateral interaction effects," Empirical Economics, Springer, vol. 28(3), pages 571-580, July.
  14. 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.
  15. Charlotte Emlinger & Florence Jacquet & Emmanuelle Chevassus Lozza, 2008. "Tariffs and other trade costs: assessing obstacles to Mediterranean countries' access to EU-15 fruit and vegetable markets," European Review of Agricultural Economics, Foundation for the European Review of Agricultural Economics, vol. 35(4), pages 409-438, December.
  16. 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.
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