Identifying the Sources of Local Productivity Growth
使用企业层面的全要素生产率指标，而非就业代理变量，估计地方动态外部性的来源，发现产业专业化和规模指标促进生产率增长，而产品多样性和竞争程度无显著影响，并指出以往基于就业的回归存在识别问题。
Using firm-level based TFP indicators (as opposed to employment-based proxies) we estimate the effects of alternative sources of dynamic externalities at the local level. In contrast to previous empirical work, we find that industrial specialization and scale indicators affect TFP growth positively, while neither product variety nor the degree of local competition have any effect. Employment-based regressions yield nearly the opposite results, in line with most of previous empirical work. We argue that such regressions suffer from serious identification problems when interpreted as evidence of dynamic externalities. Our results question the conclusions of most of the existing literature on dynamic agglomeration economies.