# Herfindahl-Hirschman Index (HHI) – Definition, Formula, and Example

## What is Herfindahl-Hirschman Index (HHI)?

The Herfindahl-Hirschman Index (HHI) is a measure of market concentration that is commonly used in economics and antitrust analysis. It provides a numerical representation of the degree of competition within a market.

The HHI is calculated by squaring the market share of each firm in the market, and then summing up the squared market shares. The resulting index ranges from 0 to 10,000, with higher values indicating greater market concentration.

For example, if a market is dominated by a single firm with a market share of 50%, the HHI would be 2,500 (50 squared). On the other hand, if a market is highly competitive with many firms having equal market shares, the HHI would be close to 0.

The HHI is often used by regulatory authorities to assess the competitiveness of a market and to determine whether mergers or acquisitions would result in a significant increase in market concentration. In general, a higher HHI indicates a less competitive market, while a lower HHI suggests a more competitive market.

By analyzing the HHI, policymakers and economists can gain insights into the level of competition within a market and make informed decisions regarding antitrust regulations and policies.

## How to Calculate Herfindahl-Hirschman Index (HHI)?

The Herfindahl-Hirschman Index (HHI) is a measure of market concentration that is calculated by summing the squares of the market shares of all firms in a given market. It is commonly used in economics and antitrust analysis to assess the level of competition in a particular industry.

To calculate the HHI, follow these steps:

1. Determine the market shares of all firms in the market. This can be done by dividing the sales revenue of each firm by the total sales revenue of all firms in the market.
2. Square the market share of each firm.
3. Sum up the squared market shares of all firms in the market.

Here is an example to illustrate the calculation of the HHI:

Firm Market Share Market Share Squared
Firm A 0.4 0.16
Firm B 0.3 0.09
Firm C 0.2 0.04
Firm D 0.1 0.01

To calculate the HHI, sum up the squared market shares:

HHI = 0.16 + 0.09 + 0.04 + 0.01 = 0.30

The resulting HHI value of 0.30 indicates a moderate level of market concentration. Generally, an HHI below 0.15 is considered low concentration, between 0.15 and 0.25 is considered moderate concentration, and above 0.25 is considered high concentration.

The Herfindahl-Hirschman Index provides a quantitative measure of market concentration and can be used to assess the level of competition in a particular industry. It is a useful tool for policymakers, regulators, and economists in evaluating market structures and potential antitrust issues.

## Why is Herfindahl-Hirschman Index (HHI) Important?

The Herfindahl-Hirschman Index (HHI) is an important measure used in economics and antitrust analysis to assess the level of market concentration. It provides valuable insights into the competitive landscape of an industry and helps regulators and policymakers make informed decisions.

There are several reasons why the HHI is important:

1. Assessing Market Power:

The HHI helps determine the level of market power held by a few dominant firms in an industry. A higher HHI indicates a more concentrated market with fewer competitors and potentially higher barriers to entry. This concentration can result in reduced competition, higher prices, and limited consumer choice.

2. Identifying Potential Anti-Competitive Behavior:

By calculating the HHI, regulators can identify industries or markets where there may be anti-competitive behavior, such as collusion or monopolistic practices. If the HHI exceeds certain thresholds, it may trigger further investigations or regulatory actions to promote fair competition.

3. Evaluating Mergers and Acquisitions:

The HHI is commonly used to evaluate the potential impact of mergers and acquisitions on market concentration. Regulators analyze the change in HHI before and after a merger to assess whether it would result in a significant increase in market power. If the post-merger HHI exceeds certain thresholds, it may prompt regulatory scrutiny or even rejection of the merger.

4. Informing Antitrust Policies:

The HHI provides policymakers with quantitative data to formulate effective antitrust policies. It helps them understand the competitive dynamics of different industries and identify sectors that require regulatory intervention to prevent market distortions or abuse of market power.

5. Promoting Consumer Welfare:

By monitoring market concentration through the HHI, regulators can protect consumer welfare. A competitive market with a lower HHI tends to offer consumers more choices, lower prices, and better quality products or services. The HHI helps ensure that markets remain competitive and that consumers are not exploited by dominant firms.

## Example of Herfindahl-Hirschman Index (HHI) Calculation

Let’s take a hypothetical example to understand how to calculate the Herfindahl-Hirschman Index (HHI). Suppose we have a market with four companies, and we know the market shares of each company:

Company A: 30%

Company B: 25%

Company C: 20%

Company D: 25%

To calculate the HHI, we need to square the market shares of each company and sum them up:

(0.30)^2 + (0.25)^2 + (0.20)^2 + (0.25)^2 = 0.09 + 0.0625 + 0.04 + 0.0625 = 0.255

The interpretation of the HHI value depends on the industry and market dynamics. Generally, an HHI below 1500 indicates a competitive market, while an HHI above 2500 suggests a highly concentrated market. HHI values between 1500 and 2500 indicate moderate concentration.

By calculating the HHI, analysts and policymakers can assess the level of competition and concentration in a market. This information can be used to identify potential antitrust concerns, evaluate market power, and make informed decisions regarding mergers and acquisitions.

Overall, the Herfindahl-Hirschman Index (HHI) provides a quantitative measure of market concentration and is a valuable tool in analyzing market competitiveness.