In this paper I assemble and array two rarely used data sets to measure the extent ofaggregate concentration the share of national economic activity accounted for by the largest X companies in the U.S. in the 1980s and 1990s. The data show clearly that, despite the substantial merger wave of the...

In this paper I present new and original evidence concerning global aggregate concentration. To my knowledge, this evidence constitutes the first systematic effort to measure global aggregate concentration. The data are available only for the years 1994-2001 and require some compromisesand...