On Theories Explaining the Success of the Gravity Equation
检验赫克歇尔-俄林理论和规模报酬递增理论能否解释引力方程在双边贸易中的成功，发现完全专业化版本被数据拒绝，不完全专业化模型表现不一，要素禀赋差异更能解释生产模式和贸易量的国际差异。
We examine whether two important theories of trade, the Heckscher-Ohlin theory and the Increasing Returns theory, can account for the empirical success of the so-called gravity equation. Since versions of both theories can predict this equation, we tackle the model identification problem by conditioning bilateral trade relations on factor endowment differences and on the share of intra-industry trade. Only for large factor endowment differences does the Heckscher-Ohlin model predict perfect production specialization in different countries as well as the gravity equation, and trade is purely in goods produced with different factor intensities. Our empirical analysis yields three findings. First, the predictions of the perfect specialization versions of both theories are rejected by the data, and so are unlikely explanations for the empirical success of the gravity equation. Second, a model of imperfect specialization that includes both increasing returns and factor endowments as sources of trade has a mixed performance: it correctly predicts more differentiated goods production when the level of intra-industry trade is greater, however, the predicted link to factor proportions in tenuous. Third, the predictions of a model with imperfect specialization that relies solely on factor endowment differs find support in the data. These results suggest that factor endowments and increasing returns explain different components of the international variation of production patterns and trade volumes.