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Demystifying modelling methods for trade policy


  • Piermartini, Roberta
  • Teh, Robert


In recent years, quantitative analysis of the effects of policies on economic outcomes has grown sharply. These exercises in quantification have been made possible by advances in theory and analytical techniques, and no less importantly, by the dramatically increased computational and data processing power of computers. This paper focuses on two classes of quantitative tools - computable general equilibrium (CGE) models and gravity models. These are perhaps the most commonly encountered quantitative analytical techniques in the area of trade. The primary purpose of this paper is to offer a non-technical explanation of CGE and gravity models to trade policymakers. We try to capture the essence of the analytical techniques, explaining the requirements of the models and computational procedures. We also seek to identify as clearly as possible the strengths and limitations of these analytical techniques. A second objective of the paper is to survey a range of studies based on CGE, particularly simulations of multilateral trade negotiations, and gravity models. The survey is useful in conveying a sense of how results can vary depending on what goes into the models by way of their structure and data, emphasizing the importance of judicious, critical interpretation. The main benefit of CGE models is that they offer a rigorous and theoretically consistent framework for analysing trade policy questions. The numbers that come out of the simulations should only be used to give a sense of the order of magnitude that a change in policy can mean for economic welfare or trade. Much more can be done to create confidence in the results. The simulations should benefit from more systematic and informative employment of sensitivity analysis. Ex-post validation of CGE models is needed to increase confidence in the numerical results. Correctly specified gravity models can illuminate questions that are important for trade policymakers. For example, what are the trade effects of WTO membership? How does entering a proposed preferential trade arrangement (PTA) affect a country's trade? How is non-members' trade affected? Does more trade lead to faster growth? Does trade improve the environment? Three important theoretical requirements that need to be taken into account in gravity models are highlighted in this study. First is the importance of relative distance and trade costs. Second is that liberalization, whether multilateral or regional, creates new trading relationships and not just increases the volume of existing trade. Third, trade is dynamic and this shows itself in new products and new firms that enter international commerce.

Suggested Citation

  • Piermartini, Roberta & Teh, Robert, 2005. "Demystifying modelling methods for trade policy," WTO Discussion Papers 10, World Trade Organization (WTO), Economic Research and Statistics Division.
  • Handle: RePEc:zbw:wtodps:10

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    References listed on IDEAS

    1. Dixon, Peter B. & Parmenter, B.R., 1996. "Computable general equilibrium modelling for policy analysis and forecasting," Handbook of Computational Economics,in: H. M. Amman & D. A. Kendrick & J. Rust (ed.), Handbook of Computational Economics, edition 1, volume 1, chapter 1, pages 3-85 Elsevier.
    2. Powell, Alan A. & Snape, Richard H., 1993. "The contribution of applied general equilibrium analysis to policy reform in Australia," Journal of Policy Modeling, Elsevier, vol. 15(4), pages 393-414, August.
    3. Francois, Joseph & van Meijl, Hans & van Tongeren, Frank, 2003. "Trade Liberalization and Developing Countries Under the Doha Round," CEPR Discussion Papers 4032, C.E.P.R. Discussion Papers.
    4. Hertel, Thomas, 1997. "Global Trade Analysis: Modeling and applications," GTAP Books, Center for Global Trade Analysis, Department of Agricultural Economics, Purdue University, number 7685.
    5. Timothy J. Kehoe, 2003. "An evaluation of the performance of applied general equilibrium models of the impact of NAFTA," Staff Report 320, Federal Reserve Bank of Minneapolis.
    6. Nguyen, T. & Perroni, C. & Wigle, R., 1993. "An Evaluation of the Final Act of the Uruguay Round," Working Papers 93003, Wilfrid Laurier University, Department of Economics.
    7. Nguyen, Trien & Perroni, Carlo & Wigle, Randall, 1993. "An Evaluation of the Draft Final Act of the Uruguay Round," Economic Journal, Royal Economic Society, vol. 103(421), pages 1540-1549, November.
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