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83 Antitrust L.J. 293 (2020-2021)
The Logic of Market Definition

handle is hein.journals/antil83 and id is 305 raw text is: THE LOGIC OF MARKET DEFINITION
For more than a half century, antitrust trials have usually begun with the
definition of a relevant market for the inquiry. Long experience has given this
exercise an air of familiarity, but closer examination reveals market definition
to be a confused exercise. Decades ago, Robert Pitofsky remarked that no
aspect of antitrust enforcement has been handled nearly as badly as market
definition.1 That sentiment remains frustratingly apt today.2 Despite its long
tenure in antitrust analysis, and despite the crucial role it has played in many a
case and investigation, the process of defining relevant markets remains both
confused and uncertain.
Why do we define markets? How should we define them? One might think
that such fundamental questions would have long been settled. But the some-
times unclear rationale for the exercise, and its inconsistent evolution in the
* David Glasner is an economist at the Federal Trade Commission, Bureau of Economics.
Sean Sullivan is associate professor of law at the University of Iowa College of Law and an
Associate Editor of the Antitrust Lw Journal. This article reflects the personal views of the
authors. It does not necessarily represent the views of the U.S. Government or Federal Trade
Commission, which have neither approved nor disapproved its content. The authors thank Chris-
tine Bartholomew, William Bishop, Aaron Edlin, Joshua Goodman, John Kirkwood, Christopher
Leslie, Matt Ralph, Daniel Sokol, Spencer Weber Waller, Gregory Werden, and conference par-
ticipants at the 2019 meeting of the American Law and Economics Association for thoughtful
comments on earlier drafts of this article. Alexander Asawa, Kassandra DiPietro, Reid Shepard,
and Madison Tallant provided superlative research assistance.
i Robert Pitofsky, New Definitions of Relevant Market and the Assault on Antitrust, 90
COLUM. L. REv. 1805, 1807 (1990); see also Donald F. Turner, The Role of the Market Con-
cept in Antitrust Law, 49 ANTITRUST L.J. 1145, 1150 (1980) (Let me turn now to what some of
the current problems are with market definition. I have to say at the outset that as a general
matter this whole area is a bloody mess.).
2 See, e.g., Louis Kaplow, Why (Ever) Define Markets?, 124 HARV. L. REv. 437, 466 (2010)
([T]here is no canonical, operational statement of the standard for determining what constitutes
a relevant market and, a fortiori, no developed underlying rationalization for whatever the princi-
ple might be.); William Blumenthal, Why Bother?: On Market Definition Under the Merger
Guidelines, Statement before the FTC/DOJ Merger Enforcement Workshop 2 (Feb. 17, 2004),
www.justice.gov/sites/default/files/atr/legacy/2007/08/30/202600.pdf ([T]he meaning of 'rele-
vant market' today ... probably is not understood by more than 500 people on the planet.).


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