The Gravity Equation in International Trade: An Explanation
The gravity equation in international trade is one of the most robust empirical finding in economics: bilateral trade between two countries is proportional to size, measured by GDP, and inversely proportional to the geographic distance between them. While the role of size is well understood, the role of distance remains a mystery. I propose the first explanation for the gravity equation in international trade, based on the emergence of a stable network of input-output linkages between firms. Over time, a firm acquires more suppliers and customers, which tend to be further away. I show that if, as observed empirically, (i) the distribution of firm sizes is well approximated by Zipf's law and (ii) larger firms export over longer distances on average, then aggregate trade is inversely proportional to distance. Data on firm level, sectoral, and aggregate trade support further predictions of the model.
I want to thank Fernando Alvarez, Michal Fabinger, Xavier Gabaix, Sam Kortum, Bob Lucas, Jim Tybout, Jon Vogel and seminar participants in Berkeley, Bilkent, Bocconi, Boston University, Chicago, Erasmus, Hitotsubashi, LBS, Louvain-CORE, LSE, the NY Fed, Oxford, Princeton, Rochester, Sciences Po, Toulouse, UBC Vancouver, Yale and Zurich for helpful discussions, and NSF grant SES-1061622 for financial support. I am indebted to Jong Hyun Chung, Stefano Mosso and Adriaan Ten Kate for their research assistance. During the last year, I have received compensation for teaching activities from the Toulouse School of Economics, as well a research grant from the National Science Foundation (SES-1061622), in excess of $10,000. The views expressed herein are those of the author and do not necessarily reflect the views of the National Bureau of Economic Research.
Thomas Chaney, 2018. "The Gravity Equation in International Trade: An Explanation," Journal of Political Economy, vol 126(1), pages 150-177.