Both Marshall and Jacobs were Right!
基于1990-2007年259个欧洲地区15个行业的数据，发现集聚外部性在技术密集型产业中更强，专业化外部性在低密度地区更强，而多样化外部性在高密度地区更重要，且雅各布斯外部性包含纯多样化和组合效应，但只有后者对区域增长有正向影响。
This article adds to the empirical evidence on the impact of agglomeration externalities on regional growth along three main dimensions. On the basis of data on 259 Europe NUTS2 (Nomenclature of Territorial Units for Statistics) regions and 15 NACE (Nomenclature statistique des Activités économiques dans la Communauté Européenne) 1.1 2-digit industries for the period 1990–2007, we show that agglomeration externalities are stronger in technology-intensive industries, also after controlling for sorting; that specialization externalities are stronger for low density regions, while diversity matters more for denser urban areas; and, finally, that Jacobs externalities comprise a pure diversification effect (related variety) and a portfolio effect (unrelated variety), although evidence of positive effects on regional growth is only found for the latter. An additional contribution of this article is to extend the analysis on the basis of a full geographical coverage of European NUTS2 regions, with the aim to generalize the empirical identification of the impacts of specialization and diversification externalities with respect to the existing literature. Our results are robust to a rich set of consistency checks, including the use of spatial autoregressive models with autoregressive disturbances, used to assess to what extent the effects of agglomeration externalities are localized.