Scale economies and the geographic concentration of industry
梳理了识别集聚经济效应的三个关键估计问题，发现两个稳健结果：本地高学历劳动力提升个人工资，产业多样化促进长期增长，支持人力资本外部性和城市多样性效应。
In recent empirical literature on spatial agglomeration, many <?Pub Caret>papers find evidence consistent with location&hyphen;specific externalities of some sort. Our willingness to accept evidence of agglomeration economies depends on how well key estimation problems have been addressed. Three issues are particularly troublesome for identifying agglomeration effects: unobserved regional characteristics, simultaneity in regional data, and multiple sources of externalities. Two empirical results appear to be robust to problems created by the first two issues: (a) individual wages are increasing in the presence of more&hyphen;educated workers in the local labor force, which is consistent with localized human&hyphen;capital externalities, and (b) long&hyphen;run industry growth is higher in locations with a wider range of industrial activities, which suggests that firms benefit from being in more diverse urban environments. Other evidence is supportive of agglomeration effects related to regional demand linkages and short&hyphen;run, industry&hyphen;specific externalities.