The Relevant Market: Possible and Productive

8 Pages Posted: 12 Apr 2014 Last revised: 11 Dec 2014

See all articles by Gregory J. Werden

Gregory J. Werden

U.S. Department of Justice - Antitrust Division

Date Written: April 11, 2014


Professor Louis Kaplow capped off his series on the relevant market with a final essay in this the Antitrust Law Journal. His premise remains that relevant market is used only to help assess a firm’s market power based on its market share. He claims: (1) “there exists no valid way to make market power inferences from shares” of a multi-product market; (2) “it is impossible to determine which market definition is superior” in inferring market power “without already formulating one’s best estimate of market power”; and (3) delineating the relevant market is “counterproductive.” This essay demonstrates the relevant market’s utility. It also shows that: (1) Kaplow’s first claim rests on a distorted view of antitrust analysis and faulty economics; (2) Kaplow does not prove his second claim, but rather just that the relevant market is not needed for the purpose he allows for it; and (3) Kaplow’s third claim rests on a misapplication of the hypothetical monopolist test, faulty economics, and erroneous facts.

Keywords: antitrust, relevant market

JEL Classification: K21, L40

Suggested Citation

Werden, Gregory J., The Relevant Market: Possible and Productive (April 11, 2014). Available at SSRN: or

Gregory J. Werden (Contact Author)

U.S. Department of Justice - Antitrust Division ( email )

450 Fifth Street, NW
9th Floor
Washington, DC 20530
United States
202-307-6366 (Phone)

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