Market power

Market power is an ability, not a synonym for size, popularity, a high price, or a positive margin. The firm must be able to influence competitive terms profitably and for a period that matters to the question.

Evidence can include substitution patterns, demand response, market shares, capacity, margins, entry and expansion, switching, contracts, direct customer or internal evidence, conduct, duration, buyer power, and natural experiments. Each measure has alternative explanations and data requirements.

Triangulate rather than crown one metric

A high share in a boundary drawn too narrowly can overstate power. A low share can obscure differentiated segments or direct effects. A price-cost margin can reflect fixed and sunk costs, risk, innovation, accounting measurement, product mix, regulation, temporary scarcity, or power. Entry history can reflect unattractive demand as well as barriers.

State the mechanism connecting evidence to profitable control over terms, test rival explanations, and report uncertainty. Accounting data should be mapped from reported segments, periods, transfer prices, allocations, and recognition rules to the economic variables actually needed.

Economic market power does not itself establish a legal violation. Current law, jurisdiction, conduct, effects, defenses, procedure, and authority remain a separate analysis.