The Evolution of US Retail Concentration
利用美国所有零售商的产品级普查数据，发现本地和全国零售集中度同步上升，多市场企业扩张是主因，本地集中度上升可解释零售毛利率增长的1/4到1/3。
Increasing national concentration has contributed to market power concerns. Yet local trends are more informative about market power in retail, where consumers have traditionally shopped at nearby stores. Using novel product-level census data for all US retailers, we find that local and national concentration increased in parallel and affect most markets, products, and industries. The expansion of multimarket firms into new markets explains most of the increase in national concentration, with consolidation via increases in local market shares increasing in importance between 1997 and 2007. Increases in local concentration can explain one-quarter to one-third of the observed rise in retail gross margins.