Identifying the Type of Market Structures

Monopoly markets and situations where companies hold significant pricing power can result in market inefficiencies, as the monopolies tend to constrain output in order to sell at higher prices. Due to this, many countries have a competition law that regulates the degree of competition in many industries.

How Do You Identify the Type of Market Structure?

Economists identify market structures by examining how firms compete within an industry. Rather than focusing only on the number of companies, they evaluate characteristics such as market concentration, pricing power, product differentiation, barriers to entry, and the number of buyers and sellers.

The four main market structures are:

• Perfect competition
• Monopolistic competition
• Oligopoly
• Monopoly

Economists also use quantitative measures such as the Concentration Ratio (CR) and the Herfindahl–Hirschman Index (HHI) to estimate how concentrated a market is and whether firms possess significant market power.

In this study note, you’ll learn how economists identify market structures using both qualitative characteristics and quantitative measures.

Key Takeaways

• Market structures are identified using both qualitative and quantitative factors.
• The number of firms alone does not determine market structure.
• Concentration Ratio measures the combined market share of the largest firms.
• HHI provides a more detailed measure of market concentration.
• High concentration does not always imply monopoly power.
• Economists also consider barriers to entry and demand elasticity.

What Factors Are Used to Identify a Market Structure?

Before calculating concentration ratios or HHI, economists first evaluate the characteristics of an industry.

The most important factors include:

These characteristics help economists determine whether an industry resembles perfect competition, monopolistic competition, oligopoly, or monopoly.

Comparing the Four Market Structures

This provides readers with a quick framework before introducing quantitative measures like concentration ratios and HHI.

Real-World Examples of Market Structure Identification

Economists frequently classify industries by comparing their competitive characteristics.

For example:

• Wheat farming is often used as an example of perfect competition because many producers sell nearly identical products.
• Restaurants typically operate under monopolistic competition because businesses differentiate themselves through menus, service, and branding.
• Commercial aircraft manufacturing resembles an oligopoly because only a few firms dominate global production.
• Local electricity distribution is commonly considered a monopoly because one provider often serves an entire region.

These examples demonstrate that identifying market structure involves evaluating multiple characteristics rather than simply counting firms.

How Do Economists Identify Market Structures?

To gauge market power, one can estimate the elasticity of demand and supply in the market. If demand is elastic, the market is close to perfect competition. On the contrary, if it is inelastic, companies may possess market power.

We can use a time series or cross-sectional regression analysis to calculate the elasticity of a market.  In a time series analysis, we observe the behavior of a parameter over an extended period, for instance, a company’s annual sales for the last 50 years. Since the market situation may have changed over the chosen period, the estimated elasticity may not reflect the current situation.

A cross-sectional analysis entails analyzing different parameters, probably from different companies, within a specific time period, such as sales from different companies within a year; This may be complicated as it requires a substantial effort to gather data from across all selected companies.

To address these issues, we employ more straightforward metrics, as discussed below.

What Is the Concentration Ratio?

The concentration ratio is the sum of market shares covered by the largest N firms in a market. It is determined by finding the sales value for the largest firms and dividing it by the total market sales.

The ratio lies between zero (for perfect competition) and 100 (for monopolies).

The main advantage of this concentration measure is the simplicity of its calculation.

What Are the Limitations of the Concentration Ratio?

1. It fails to quantify market power directly, i.e., a high concentration ratio may not necessarily mean that a firm is a monopoly. For instance, a monopoly operating in a market structure with low barriers to entry may be forced to behave (price its products) like a firm operating in perfect competition.
2. It is not affected by mergers among the top market incumbents. For instance, if the top two companies merge, their combined pricing power will be greater than that of each of the two pre-existing companies. However, the concentration ratio may not change much.

Example: Concentration Ratio

Suppose there are 10 producing companies in a 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:

Concentration ratio = 35% + 20% + 10% = 65%

What Is the Herfindahl–Hirschman Index (HHI)?

The HHI first squares the market shares of the top N companies, then sums them up. The HHI is 1 for a monopoly firm and for M firms with equal market share.

The HHI was developed to try to curb some of the limitations of the concentration ratio.

Example: Herfindahl–Hirschman Index (HHI)

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

HHI = 0.35² + 0.20² + 0.10² = 0.1725

What Are the Limitations of the HHI?

1. The HHI does not consider the elasticity of demand; thus, it cannot approximate the potential profitability of a single company or a group of companies.
2. HHI does not take the possibility of entry into account.

Which Measure Is Better: Concentration Ratio or HHI?

Both measures help economists evaluate market concentration, but each serves a different purpose.

The Concentration Ratio provides a quick estimate of how much of the market is controlled by the largest firms.

The HHI provides a more detailed measure because it gives greater weight to firms with larger market shares.

In practice, economists often use both measures together when evaluating competition within an industry.

CFA Exam Tip

The CFA exam frequently tests your ability to distinguish between market structures and identify the most appropriate measure of market concentration.

Remember:

• Concentration Ratio = Sum of the largest firms’ market shares.
• HHI = Sum of squared market shares.
• Higher HHI generally indicates greater market concentration.
• Neither measure alone proves monopoly power.

Question

Which of the following best describes a market structure with only one buyer?

1. Monopoly.
2. Monopsony.
3. Monopolistic competitive market.

Solution

The correct answer is B.

A monopsony has only one buyer.

A is incorrect. A monopoly has one seller but many buyers.

C is incorrect. A monopolistic competitive market has many buyers and fairly many sellers.

Question

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

1. Concentration ratio = 4%; HHI = 40.
2. Concentration ratio = 40%; HHI = 0.08.
3. Concentration ratio = 40%; HHI = 0.4.

Solution

The correct answer is B.

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

Therefore, \(20\% + 20\% = 40\%\).

For the HHI, we take \({0.20}^2 \times 2 = 0.08\).

Frequently Asked Questions

How do economists identify a market structure?

Economists evaluate the number of firms, market concentration, pricing power, product differentiation, barriers to entry, and competition within an industry.

What are the four main market structures?

The four primary market structures are perfect competition, monopolistic competition, oligopoly, and monopoly.

What is the Concentration Ratio?

The Concentration Ratio measures the combined market share of the largest firms in an industry.

What is the Herfindahl–Hirschman Index (HHI)?

The HHI measures market concentration by summing the squared market shares of firms within an industry.

Why is HHI better than the Concentration Ratio?

HHI accounts for differences in firm size because larger firms receive greater weight through squaring their market shares.

Does a high concentration ratio always indicate monopoly?

No. High concentration may indicate significant market power, but firms may still face competition from potential entrants or substitute products.

What is a monopsony?

A monopsony is a market structure with a single buyer and many sellers.

Why Identifying Market Structures Matters in CFA Level I

Understanding how economists classify market structures is essential for analyzing competition, pricing power, profitability, and long-run industry behavior.

Candidates should be able to distinguish between qualitative characteristics and quantitative measures such as Concentration Ratios and the Herfindahl–Hirschman Index when evaluating market power.