The Herfindahl-Hirschman Index (HHI) is defined as the sum of the squares of the market shares of all firms within the industry, where the market shares are expressed as fractions. As a general rule, an HHI below 1,000 signals low concentration, while an index above 1,800 signals high concentration. For values between 1,000 and 1,800, an industry is considered to be moderately concentrated.
The range of the index lies between 0 and 10 000. 6  See B. Cœuré (2014), “On the optimal size of the financial sector”, speech at the ECB conference on the optimal size of the financial sector, Frankfurt, 2 September. BIS central bankers’ speeches  3  Regulatory environment This brings me to the second part of my remarks: the regulatory environment.