Final answer:
No, it is not true. The Four-Firm Concentration Ratio puts more emphasis on one or two very large firms, while the Herfindahl-Hirschman Index puts more emphasis on all the firms in the entire market.
Step-by-step explanation:
No, it is not true. The Four-Firm Concentration Ratio and the Herfindahl-Hirschman Index (HHI) are two measures used to assess the level of competition in an industry. While both measures consider market share, they differ in their emphasis on the size of firms. The Four-Firm Concentration Ratio puts more emphasis on one or two very large firms, while the HHI puts more emphasis on all the firms in the entire market.
For example, let's say we have four firms in the industry, and their market shares are as follows: A - 40%, B - 30%, C - 20%, D - 10%. The Four-Firm Concentration Ratio would focus on the market shares of firms A and B, which have the largest shares. In contrast, the HHI would consider the market shares of all four firms, giving more weight to the smaller firms (C and D) as well.
Therefore, big cross-company rating differences in a region may not always significantly account for company-to-company differences in branded pairs sold and market share in all regions, as the emphasis on firm size varies depending on the measure used.