Gravity with Gravitas: A Solution to the Border Puzzle
指出传统引力方程缺乏理论基础，导致估计有偏，并开发了新方法一致估计理论引力方程，正确计算贸易摩擦的比较静态，应用于解决McCallum边界谜题，发现工业化国家间边界使贸易减少20-50%。
Gravity equations have been widely used to infer trade flow effects of various institutional arrangements. We show that estimated gravity equations do not have a theoretical foundation. This implies both that estimation suffers from omitted variables bias and that comparative statics analysis is unfounded. We develop a method that (i) consistently and efficiently estimates a theoretical gravity equation and (ii) correctly calculates the comparative statics of trade frictions. We apply the method to solve the famous McCallum border puzzle. Applying our method, we find that national borders reduce trade between industrialized countries by moderate amounts of 20–50 percent.