IDEAS home Printed from
   My bibliography  Save this paper

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.

Suggested Citation

  • Haq, Zahoor Ul & Meilke, Karl D. & Cranfield, John A.L., 2011. "The Gravity Model and the Problem of Zero`s in Agrifood Trade," Working Papers 116851, Canadian Agricultural Trade Policy Research Network.
  • Handle: RePEc:ags:catpwp:116851

    Download full text from publisher

    File URL:
    Download Restriction: no

    References listed on IDEAS

    1. repec:wsi:wschap:9789813144415_0017 is not listed on IDEAS
    2. Muhammed Dalgin & Vitor Trindade & Devashish Mitra, 2008. "Inequality, Nonhomothetic Preferences, and Trade: A Gravity Approach," Southern Economic Journal, Southern Economic Association, vol. 74(3), pages 747-774, January.
    3. Sampath Jayasinghe & John C. Beghin & Giancarlo Moschini, 2017. "Determinants Of World Demand For U.S. Corn Seeds: The Role Of Trade Costs," World Scientific Book Chapters,in: Nontariff Measures and International Trade, chapter 17, pages 309-320 World Scientific Publishing Co. Pte. Ltd..
    4. 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.
    5. Buch, Claudia M. & Kleinert, Jorn & Toubal, Farid, 2004. "The distance puzzle: on the interpretation of the distance coefficient in gravity equations," Economics Letters, Elsevier, vol. 83(3), pages 293-298, June.
    6. Gaël 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;Association for Comparative Economic Studies, vol. 45(4), pages 520-536, December.
    7. Wang, Zhen Kun & Winters, L. Alan, 1991. "The Trading Potential of Eastern Europe," CEPR Discussion Papers 610, C.E.P.R. Discussion Papers.
    8. 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.
    9. 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.
    10. 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.
    11. 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.
    12. J. M. C. Santos Silva & Silvana Tenreyro, 2006. "The Log of Gravity," The Review of Economics and Statistics, MIT Press, vol. 88(4), pages 641-658, November.
    13. 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.
    14. 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.
    15. Elhanan Helpman & Marc Melitz & Yona Rubinstein, 2008. "Estimating Trade Flows: Trading Partners and Trading Volumes," The Quarterly Journal of Economics, Oxford University Press, vol. 123(2), pages 441-487.
    16. 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.
    17. 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.
    18. Peter Egger, 2002. "An Econometric View on the Estimation of Gravity Models and the Calculation of Trade Potentials," The World Economy, Wiley Blackwell, vol. 25(2), pages 297-312, February.
    Full references (including those not matched with items on IDEAS)


    Citations are extracted by the CitEc Project, subscribe to its RSS feed for this item.

    Cited by:

    1. Chen, Yiu Por (Vincent), 2015. "Fiscal Decentralization, Rural Industrialization, and Undocumented Labor Mobility in Rural China (1982-87)," IZA Discussion Papers 9024, Institute for the Study of Labor (IZA).


    All material on this site has been provided by the respective publishers and authors. You can help correct errors and omissions. When requesting a correction, please mention this item's handle: RePEc:ags:catpwp:116851. See general information about how to correct material in RePEc.

    For technical questions regarding this item, or to correct its authors, title, abstract, bibliographic or download information, contact: (AgEcon Search). General contact details of provider: .

    If you have authored this item and are not yet registered with RePEc, we encourage you to do it here. This allows to link your profile to this item. It also allows you to accept potential citations to this item that we are uncertain about.

    If CitEc recognized a reference but did not link an item in RePEc to it, you can help with this form .

    If you know of missing items citing this one, you can help us creating those links by adding the relevant references in the same way as above, for each refering item. If you are a registered author of this item, you may also want to check the "citations" tab in your RePEc Author Service profile, as there may be some citations waiting for confirmation.

    Please note that corrections may take a couple of weeks to filter through the various RePEc services.

    IDEAS is a RePEc service hosted by the Research Division of the Federal Reserve Bank of St. Louis . RePEc uses bibliographic data supplied by the respective publishers.