Most product markets are local. The reason is simply that the transportation of goods and people is costly so firms set up production plants, distribution centers, and stores close to customers. In turn, individuals locate in areas where they can obtain the goods they desire. A coffee shop or restaurant in Manhattan does not compete with similar establishments in Seattle and probably not even in Brooklyn. The wedge in prices created by the inconvenience and monetary cost of buying a product far away from the desired consumption point shields companies in different locations from direct competition. Of course, the size of these costs and, therefore, the geographic extent of the market vary by product. Markets are also product specific. Producers of a particular product are shielded from competition by producers of distinct but related goods and services to the degree that their consumption requires households to move away from their ideal variety. Much has been written recently about the increase in national market concentration observed over the last 2 decades and the role that large national firms have played in driving this trend. The evidence for the rise in concentration is uncontroversial; the shares of the largest firms and the Herfindahl-Hirschman Index (HHI), among other measures of concentration, have increased consistently in most sectors since 1990. A narrative has emerged whereby this increase in national concentration is perceived as the cause of lower product-market competition. This fall in competition is then viewed as the culprit of other apparent trends, such as rising markups andmarket power (Gutiérrez and Philippon 2017; Hall 2018; De Loecker,

中文翻译：

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国家和地方集中度的不同趋势

大多数产品市场都是本地的。原因很简单，货物和人员的运输成本很高，因此公司在靠近客户的地方设立了生产工厂、配送中心和商店。反过来，个人定位在他们可以获得他们想要的商品的区域。曼哈顿的咖啡店或餐厅不与西雅图的类似场所竞争，甚至在布鲁克林也可能不存在。购买远离所需消费点的产品所带来的不便和货币成本造成的价格楔子使不同地区的公司免受直接竞争。当然，这些成本的大小以及市场的地理范围因产品而异。市场也是特定于产品的。特定产品的生产者免受不同但相关的商品和服务生产者的竞争，以至于他们的消费要求家庭远离他们的理想品种。最近有很多关于过去 2 年观察到的国家市场集中度的增加以及大型国家公司在推动这一趋势中所起的作用的文章。浓度上升的证据是无可争议的；自 1990 年以来，在大多数行业中，最大公司的份额和赫芬达尔-赫希曼指数 (HHI) 以及其他集中度指标一直在增加。出现了一种说法，即这种国家集中度的增加被认为是产品下降的原因——市场竞争。这种竞争下降被视为其他明显趋势的罪魁祸首，