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Census of Manufactures. Concentration Ratios in Manufacturing
1987 - U.S. Documents C 3.24/12: MC 87-S-6
1982 - U.S. Documents C 3.24/12: MC 82-S-7
1977 - U.S. Documents C 3.24/12: MC 77-SR-9
1972 - U.S. Documents C 3.24: 972/v.1x (Subject & Special Statistics, pages SR2-1 through SR2-240)
1967 - U.S. Documents C 3.24/15: 967/ 2.1-4
Herfindahl-Hirschman Index for 50 largest companies
is only included in the manufacturing reports.
was shown for the first time in the 1982 Concentration Ratios in Manufacturing.
is calculated by squaring the concentration ratio for each of the top 50 companies or the entire universe (whichever is lower), and summing those squares to a cumulative total.
The higher the index, the more concentrated the industry group or industry is at the top. For example, consider an industry where the concentration ratio for the top 50 companies is 100. From the concentration ratio, it is impossible to determine the amount accounted for by the top ranked companies. The Herfindahl-Hirschman Index would provide an insight to this determination. If each of the top 50 companies accounted for 2 percentage points of the 100 percent, the index would be 200. However, if the top ranked company accounted for 50 percentage points, and the remaining 49 companies slightly more than 1 percentage point each, the index would be 2550.
The above description of the Herfindahl-Hirschmann Index appeared in the 1987 Concentration Ratios in Manufacturing, page xi.