Non-linear externalities in firm localization
构建模型区分地区固有优势与本地化外部性，允许外部性呈二次型，通过意大利通勤区数据检验发现二次项几乎不显著，表明线性模型足以近似本地化外部性。
Non-linear externalities in firm localization. Regional Studies. This paper presents a model of firm localization in which the intrinsic advantages of regions are disentangled from localized externalities, while this latter force is allowed to have a quadratic shape. Through inferential analysis, it is verified whether the quadratic component of localized externalities is statistically different from zero. Such a term can reflect more-than-linear positive feedbacks as well as congestion effects, so that the sign of the interdependencies stemming from localization is not assumed a priori to be positive. The main result is that the quadratic term is virtually never statistically different from zero across Italian sectors observed at the scale of commuting zones, so that localized externalities seem to be well approximated by a linear specification.