Aggregate Concentration in Corporate America: The Case of the Fortune 500

This article provides a look at business concentration for sales and assets for the period 1967 to 2002 based on Theil’s entropy, a measure adopted by several authors in earlier publications. For contrast, three other well-known measures of concentration, the Hirschman-Herfindahl (HHI) index and the 4-firm and 8-firm concentration ratios, CR4 and CR8, were utilized. Data used were sales and assets of the largest 500 companies provided by Fortune magazine. In addition to detailed results on concentration, the paper found that the inclusion of service firms with the industrial firms in the list of 500 in 1994 somewhat changed the levels and trends in concentration.