Example of a hypothetical concentration ratio
The following are the annual sales, in £m, of the six firms in a hypothetical market:
A = 56
B = 43
C = 22
D = 12
E = 3
F = 1
In this hypothetical case, the 3-firm concentration ratio is 88.3%, that is 121/137 x 100.
Example - Telephone services
While there are around 170 telephone service suppliers in the UK (Source: simplyswitch.com), the fixed-line market is dominated by two main suppliers, BT and Virgin Media, with a 3-firm concentration ratio for fixed-line telephone supply of 89% in 2006.
Example - Fuel retailing
The Herfindahl – Hirschman Index (H-H Index)
This is an alternative method of measuring concentration and for tracking changes in the level of concentration following mergers. The H-H index is found by adding together the squared values of the % market shares of all the firms in the market. For example, if three firms exist in the market the formula is X2 + Y2 + Z2; where X, Y and Z are the percentages of the three firm’s market shares.
If the index is below 1000, the market is not considered concentrated, while an index above 2000 indicates a highly concentrated market or industry – the higher the figure the greater the concentration.
Mergers between oligopolists increase concentration and ‘monopoly power’ and are likely to be the subject of
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