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Gravity or Dummies? The Limits of Identification in Gravity Estimations


  • Cecília Hornok


Trade economists often estimate gravity equations of international trade with fixed effects. Anderson and van Wincoop (2003, American Economic Review 93, 170–192) have shown the importance of controlling for multilateral trade resistances when estimating a gravity equation. This can be done by including exporter-time and importer-time fixed effects in a panel or exporter and importer fixed effects in a cross section estimation. I argue that this approach limits the identifiability of policy parameters that capture the effect of certain ”club memberships” (EU, NAFTA, euro area, WTO, etc.) on trade flows. I show that, in the baseline case, only one effect can be identified, which precludes, for example, the estimation of separate effects on the exporter and the importer side. The magnitude, and even the sign, of the estimated club effect are very sensitive to the precise identification assumptions, which are often left unspecified in empirical studies. The underlying problem is that club membership provides some, but very little bilateral variation. When heterogeneous club effects are to be identified, the membership dummies can become perfectly collinear with the fixed effects. Empirical researchers may not be aware of the lack of identification, because standard estimation techniques often permit them to run perfectly collinear regressions. I illustrate the findings with estimating the effect of EU enlargement in 2004 on the trade flows of new and old members. Finally, I discuss potential solutions.

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  • Cecília Hornok, 2012. "Gravity or Dummies? The Limits of Identification in Gravity Estimations," CEU Working Papers 2012_11, Department of Economics, Central European University, revised 20 May 2012.
  • Handle: RePEc:ceu:econwp:2012_11

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    References listed on IDEAS

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    Cited by:

    1. Sébastien Miroudot & Ben Shepherd, 2014. "The Paradox of ‘Preferences’: Regional Trade Agreements and Trade Costs in Services," The World Economy, Wiley Blackwell, vol. 37(12), pages 1751-1772, December.
    2. P. Montalbano & S. Nenci, 2014. "Assessing the trade impact of the European Neighbourhood Policy on the EU-MED Free Trade Area," Applied Economics, Taylor & Francis Journals, vol. 46(7), pages 730-740, March.
    3. Matyas, Laszlo & Balazsi, Laszlo, 2011. "The estimation of three-dimensional fixed effects panel data models," MPRA Paper 34976, University Library of Munich, Germany.
    4. Maria Cipollina & Luca De Benedictis & Luca Salvatici & Claudio Vicarelli, 2016. "Policy Measurement And Multilateral Resistance In Gravity Models," Working Papers LuissLab 16130, Dipartimento di Economia e Finanza, LUISS Guido Carli.
    5. László Mátyás & László Balázsi, 2012. "The Estimation of Multi-dimensional Fixed Effects Panel Data Models," CEU Working Papers 2012_2, Department of Economics, Central European University, revised 18 Feb 2013.
    6. Maria Cipollina & Luca Salvatici & Luca De Benedictis & Claudio Vicarelli, 2013. "A note on dummies for policies in gravity models: a Montecarlo experiment," Departmental Working Papers of Economics - University 'Roma Tre' 0180, Department of Economics - University Roma Tre.
    7. Lavinia Rotili, 2014. "The Euro effects on intermediate and final exports," Working Papers 7/14, Sapienza University of Rome, DISS.

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