Market Concentration – Measurement Approaches and Interpretation

Introduction

Market concentration refers to the degree to which market share is distributed among participants. A concentrated market has a few large firms holding most of the share. A fragmented market has many small firms, each with a small share. Concentration is a descriptive statistic, not a verdict on market performance. This article describes how concentration is measured, the limitations of each measure, and how to interpret concentration figures without making premature normative claims.

Why Measure Concentration

Consultants measure concentration for several bounded purposes: comparing markets over time, screening for potential competition concerns, or describing industry structure. Concentration alone does not prove the presence or absence of market power. It is an input, not a conclusion.

Common Concentration Measures

1. Concentration Ratios (CRn)
The CRn sums the market shares of the largest n firms. The most common are CR3 and CR5.

• Calculation: CR3 = s1 + s2 + s3, where s is market share
• Range: 0% to 100%
• Example: Three firms with shares 30%, 25%, 20% produce CR3 = 75%

Advantages: Simple, intuitive, requires minimal data.
Limitations: Ignores the distribution among the top n firms (30/25/20 vs. 40/30/5 both yield 75% CR3). Ignores the tail of smaller firms entirely.

2. Herfindahl-Hirschman Index (HHI)
The HHI sums the squares of all firms' market shares, typically expressed in points (multiply by 10,000).

• Calculation: HHI = Σ (share_i)^2 × 10,000
• Range: Near 0 (many tiny firms) to 10,000 (pure monopoly)
• Example: Shares 30%, 25%, 20%, 15%, 10% → squares: 900 + 625 + 400 + 225 + 100 = 2,250 HHI

Advantages: Gives more weight to larger firms (due to squaring). Uses all firms, not just top n.
Limitations: Requires complete market share data for all firms. Interpretation thresholds are convention-based, not mathematical.

Conventional thresholds (U.S. Horizontal Merger Guidelines):

• Below 1,500: Unconcentrated
• 1,500 to 2,500: Moderately concentrated
• Above 2,500: Highly concentrated

These thresholds are regulatory conventions, not economic laws. Other jurisdictions use different numbers.

Choosing Between Measures

The appropriate measure depends on the question:

• CR3 is sufficient for rough description or when tail data is unavailable
• HHI is preferred for merger screening or when the distribution of shares among top firms matters
• CR1 (top firm share alone) may be relevant for markets with a single dominant participant

No single measure is universally superior.