External effects in U.S. procyclical productivity
发现美国制造业整体的规模报酬估计值大于两位数行业，这种差异源于仅在加总层面内部化的因素，即外部效应，从而排除了仅靠自身投入变化解释顺周期生产率的可能性。
In this paper we highlight a new dimension of the aggregate procyclical productivity phenomenon. We show that estimates of the degree of returns to scale are larger for manufacturing as a whole than for two-digit industries. Since this difference must be due to factors that are only internalized at the most aggregate level, we term it an external effect. This result rules out explanations based on own-input variation —such as true increasing returns and unmeasured factor utilization tied to own-activity —as the sole explanations for aggregate procyclical productivity. We explore several potential explanations of this external effect.