## Concentration Ratio

The concentration ratio is the sum of market shares covered by the largest N firms. It requires one to find the sum of the value of sales for the largest firms and divides them by the total market sales. Therefore, the resulting figure lies between zero (for perfect competition) and 100 (for monopolies).

The main advantage of this concentration measure is the fact that it is simple to calculate. However, there are some limitations to using this method.

### Example of Concentration Ratio

Suppose that there are 10 producing companies in the market. The production percentages for the top-three companies are 35%, 20%, and 10%. Calculate the concentration ratio for these three companies.

#### Solution

The concentration ratio is the sum of market shares covered by the largest N firms. So the concentration ratio for the first 3 companies are:

$$\text{Concentration ratio} = \frac{35\%+20\%+10\%}{100%}=65%$$

### Limitations of the Concentration Ratio

This method cannot quantify market power directly. The big question should be whether high concentration levels can be interpreted as an indication of monopoly power. An example is the case of only one sugar company in a country. This company enjoys monopoly power as the sugar company. However, the problem comes in when there exist large wholesalers in, say, the food sector. These wholesalers may decide to be importing sugar alongside their range of products. As a result, this will most likely convince the sugar company to set its prices like it’s in perfect competition.

The concentration ratio tends not to be affected by mergers in the top market incumbents. If there exists a merger between the largest and second-largest companies, their combined pricing power is most likely to be larger than that of the two pre-existing companies, which will not be accurately represented by the concentration ratio.

## The Herfindahl–Hirschman Index (HHI)

Economists O.C. Herfindahl and A.O. Hirschman came up with an index which first squares the market shares of top companies. These squares are then summed up. For a monopoly firm, the Herfindahl-Hirschman Index (HHI) should be equal to 1.

Consequently, in the case of firms with equal market shares, the HHI should be equal to $$\frac{1}{M}$$. This is a very useful gauge for interpreting the HHI. This measure was developed to try and overcome some issues associated with the concentration ratio.

### Example of the Herfindahl–Hirschman Index (HHI)

Using the same example as above, the HHI for the top three companies can be calculated as:

$$\text{HHI} = 0.35^2+0.20^2+0.10^2=0.195$$

### Limitations of the HHI

The HHI does not consider the elasticity of demand and thus it cannot be used to approximate the potential profitability of a single company or a group of companies.

## Question 1

If a market has 5 suppliers and the top two suppliers each hold 20 percent of the market share, which of the following best represents the concentration ratio for the top 2 suppliers and their respective HHI?

A.  Concentration ratio = 4%; HHI = 40

B.  Concentration ratio = 40%; HHI = 0.08

C.  Concentration ratio = 40%; HHI = 0.4

Solution

The concentration ratio is a sum of the two suppliers’ market share.

Therefore, 20% + 20% = 40%.

For the HHI, we take 0.202 × 2 = 0.04.

## Question 2

Which one of the following is least likely a characteristic of the concentration ratio measure?

A. It is simple to compute

B. It does not directly quantify market power

C. It cannot be used to estimate elasticity

Solution

As a matter of fact, analysts use the simpler concentration to estimate elasticity. On the other hand, the HHI does not consider the elasticity of demand and thus it cannot be used to approximate the potential profitability of a single company or a group of companies

Describe the use and limitations of concentration measures in identifying market structure

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