The Gravity Equation in International Trade: An Explanation
提出国际贸易引力方程的第一个理论解释，基于进出口商接触网络的动态形成，说明距离如何通过阻碍初始联系获取而影响贸易，并用企业、行业和总体贸易数据验证模型预测。
The gravity equation in international trade is one of the most robust empirical finding \nin economics: bilateral trade between two countries is proportional to their respective sizes, \nmeasured by their GDP, and inversely proportional to the geographic distance between them. \nWhile the role of economic size is well understood, the role played by distance remains a mystery. \nIn this paper, I propose the first explanation for the gravity equation in international \ntrade. This explanation is based on the emergence of a stable international network of importers \nand exporters. Firms can only export into markets in which they have a contact. They \nacquire contacts by gradually meeting the contacts of their contacts. I show that if, as observed \nempirically, (i) the distribution of the number of foreign countries accessed by exporters is fat \ntailed, (ii) there is a large turnover in exports, with firms often going in and out of individual \nforeign markets, and (iii) geographic distance hinders the initial acquisition of contacts \nin an arbitrary way, then trade is proportional to country size, and inversely proportional to \ndistance. Data on firm level, sectoral, and aggregate trade support further predictions of the \nmodel.