内容简报
Employment growth in eight specific manufacturing industries in 224 metropolitan areas between 1970 and 1987.
结论we find only MAR externalities for mature industries and both MAR and Jacobs externalities for new high-tech industries—that are consistent with notions of persistence and urban product cycles.
精彩句段
There are two types of static externalities: localization economies in which a firm benefits from local firms in just the same industry, and urbanization economies in which a firm benefits from overall local urban scale and diversity.
There are two types of dynamic externalities. With terminology used in Glaeser et al. (1992), dynamic externalities may be Marshall-Arrow-Romer (MAR) (localization) economies, which derive from a buildup of knowledge associated with ongoing communications among local firms in the same industry, or Jacobs (1969) (urbanization) economies, which derive from a buildup of knowledge or ideas associated with historical diversity. (非常喜欢，赞同。)
Cities with historical concentrations of an industry and related local knowledge accumulations will offer a more productive environment for establishments in that industry than those without them. They will be able to better compete for and, over time, retain plants and employment in that industry.
New high-tech industries are more likely to take root in cities with a history of industrial diversity suggesting that Jacobs externalities are important for these industries.
第一部分：传统制造业
模型是怎么来的？
We model 1987 city employment in each industry as a function of historical and current conditions in cities.
W_it=A_it (∙)f^' (N_it;…)P_it (∙)
P_it (∙)=P(N_it,〖MC〗_it)
〖MC〗_it includes regional characteristics, access to major urban market centers, and local metro area demand for capital good products.
A_it (∙)=A(N_it,N_i0,ρ_i0,D_i0)
ρ_i0 is the concentration of that employment. D_i0 is the diversity of the environment.
所以
N_it=N(W_it,〖MC_it,N〗_i0,ρ_i0,D_i0,…)
左边可以处理为就业增长率。〖log(N〗_it/N_i0)=N ̃(∙)
指标
Concentration is to represent MAR externalities more directly since it facilitates spillovers or “network” information flows among relevant firms. Past concentration is measured by the ratio of own industry employment to total local civilian employment in 1970. 另外的集中度指数The ratio of own industry employment to total local effective urban land area.
The own industry level measure represents remaining persistence in employment level.
Hirschman-Herfindahl index for about 50 three-digit manufacturing industries.
HHI_ik=∑_(j∉k)▒s_ij^2
Where i is city and k is industry. s_ij is the share in city i of three-digit manufacturing industry j in local all other manufacturing employment.
控制变量: 产出和劳动力市场条件
Regional dummies: 1970 employment.
An access measure: distance from an MSA to the nearest of the 30 Rand McNally national business centers.
A measure of local demand for the industry: the employment in all other manufacturing.
Current wage
Educational attainment
Current economic conditions: state fuel and electrical prices, diversity of the local industrial environment, median residential rents, coastal location, and contiguity of PMSAs in a consolidated metropolitan area.
使用Heckman-type selection test检验选择性偏误，怎么做？
第二部分：高科技产业
While major two-digit industries have positive employment in virtually all cities, our three high-tech industries do not. Given this, a discrete-continuous choice analysis is more appropriate than a Tobit formulation. The discrete event is whether a city has an industry or not in 1987 and conditional on that the continuous event is the employment level in equation (1). For the discrete event, on the basis of the wage equals VMP equation from section I, for cities with the industry (I =1 vs 0) we are estimating,
prob(I_it=1)=prob[W_it<A_it (∙)f^' (N ̃_it,…)P_it (∙)]
N ̃_it is some minimal employment level or Inada conditions do not apply.
评论
针对因变量的特征，分别选择了Tobit模型和logit/probit模型。
同样的，影响就业的不仅有需求因素，还有供给因素。作者只考虑了第一个方面。
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