Lerner Index

Measuring market power through price-cost margins — A key metric in antitrust economics

Market Power Indicator Moderate Power
0.20
Lerner Index (L)
0 (Perfect Competition) 1 (Pure Monopoly)

Moderate Market Power

A Lerner Index of 0.20 suggests meaningful market power. Firms can sustain prices above marginal cost. This could indicate product differentiation, barriers to entry, or oligopolistic coordination. Mergers here warrant careful competitive effects analysis.

Price & Cost Inputs
Market Price (P) $100
Marginal Cost (MC) $80
L = (P - MC) / P
$20
Price - MC
÷
 
$100
Price
=
 
0.20
Lerner Index

Elasticity Relationship

L = 1 / |ε|

For a profit-maximizing firm, the Lerner Index equals the inverse of the absolute value of demand elasticity. This means firms with more inelastic demand can charge higher markups—a key insight for market definition.

Implied Elasticity: |ε| = 5.00

Market Structure Benchmarks
🏪
Perfect Competition
L ≈ 0
Many firms, homogeneous products, price = MC
🏢
Monopolistic Competition
L = 0.1-0.3
Many firms, differentiated products, some pricing power
🏭
Oligopoly
L = 0.3-0.6
Few firms, strategic interdependence, significant markups
🏰
Monopoly
L = 0.5-0.9
Single firm, maximum market power, highest markup