Trade, Gravity, and Aggregation
研究了从加总引力方程中恢复部门层面参数的可能性，发现当贸易成本回归量不随部门变化时，加总估计量可解释为部门弹性的加权平均，否则存在偏差但方向可推断。
Abstract Gravity equations are an important tool in empirical international trade research. We study to what extent sector-level parameters can be recovered from aggregate gravity equations estimated via Poisson pseudo maximum likelihood. We show that in the leading case where trade cost regressors do not vary at the sector level, estimates obtained with aggregate data have a clear interpretation as a weighted average of sectoral elasticities. Otherwise the estimates are biased, but researchers may possibly infer the direction of the bias. We illustrate our results by revisiting Baier and Bergstrand’s (2007) influential study of the effects of free trade agreements.