Scale economies, returns to variety, and the productivity of public infrastructure
研究公共基础设施在一般均衡背景下如何影响制造业生产率，发现基础设施通过增加制造业多样性（企业数量）间接提升生产率，而非直接作用于产出。
We examine the productivity of public infrastructure in a general equilibrium context. In our model, infrastructure lowers costs in a manufacturing sector characterized by both firm-level returns to scale and industry-level external returns to variety. Infrastructure alters factor prices, intermediate prices and the allocation of factors across sectors. However, the effect on manufacturing or aggregate output is indeterminate. In particular, our theory suggests that the degree of monopoly power influences public capital's productivity effect. We test the model using state-level, panel data. We confirm the absence of direct effects on output, but find evidence to suggest a positive impact of public capital on manufacturing variety as measured by the number of manufacturing establishments. These results indicate the need for future research on potentially important indirect channels by which public capital affects manufacturing productivity.