Productivity Differences Between and Within Countries
记录了美洲多国国内（跨市）收入差异，发现人力资本无法解释其中很大一部分，并提出一个模型将国家间技术差异与国内生产效率差异联系起来。
We document substantial within-country (cross-municipality) differences in incomes for a large number of countries in the Americas. A significant fraction of the within-country differences cannot be explained by observed human capital. We conjecture that the sources of within-country and between-country differences are related. As a first step toward a unified framework, we propose a simple model incorporating differences in technological know-how across countries and differences in productive efficiency within countries.