Does counting imports change whether U.S. manufacturing concentration has risen?
Core argument: The top 20 U.S. manufacturing firms' production concentration — their sales as a share of U.S. production, excluding imports but including exports — rose between 1992 and 2012.
Previous studies have focused on what we refer to as production concentration, which is measured as the sales of the largest U.S. producers as a share of total production in the U.S. It does not take account of imported goods, but does include U.S. firms’ exports. As shown in the chart, the production concentration of the top twenty firms has increased between 1992 and 2012 (blue line). For questions related to market power in the product market, we need to take into account the sales of foreign exporters in the United States (and exclude U.S. firms’ sales abroad). We refer to this measure of concentration as market concentration. The chart [based on confidential census data] shows that the largest [20] firms’ (which could be U.S. or foreign) share of total sales (inclusive of sales by foreign firms) in U.S. manufacturing industries has been flat in the aggregate (red line). Our finding that U.S. firms’ market share has fallen suggests that the market power of U.S. manufacturing firms may actually have declined over the past few decades.



