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Market Definition: Use and Abuse


  • Dennis W. Carlton

    (Economic Analysis Group, Antitrust Division, Department of Justice)


A “market” can be rigorously and precisely defined quantitatively, but the information to do so is typically not available. Instead, markets are often defined based on qualitative information, leading to the possibility of errors. I make some practical suggestions to mitigate such errors. When markets are correctly defined, it is the change in market shares that is central to the antitrust analysis, though this is not how courts typically use market definition and shares to analyze Section 2 cases. Unfortunately, there is only a weak link between change in market share and change in competitive performance, and that is why market definition and the use of market shares are very crude tools of analysis. That is why their best use is as safe harbors to quickly screen out frivolous cases from those where the economic forces governing industry behavior need to be carefully studied. But, I explain why even this use of market definition and market shares can be problematic in Section 2 cases.

Suggested Citation

  • Dennis W. Carlton, 2007. "Market Definition: Use and Abuse," EAG Discussions Papers 200706, Department of Justice, Antitrust Division.
  • Handle: RePEc:doj:eagpap:200706

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    References listed on IDEAS

    1. David Evans & Richard Schmalensee, 2007. "The Industrial Organization of Markets with Two-Sided Platforms," CPI Journal, Competition Policy International, vol. 3.
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    Cited by:

    1. Reurink, Arjan, 2016. "Financial fraud: A literature review," MPIfG Discussion Paper 16/5, Max Planck Institute for the Study of Societies.
    2. Dennis Carlton & Ken Heyer, 2007. "The Year in Review: Economics at the Antitrust Division, 2006–2007," Review of Industrial Organization, Springer;The Industrial Organization Society, vol. 31(2), pages 121-137, September.
    3. Hongjai Rhee & Minsoo Park, 2011. "Fixed-to-mobile call substitution and telephony market definition in Korea," Journal of Regulatory Economics, Springer, vol. 40(2), pages 198-218, October.
    4. Dennis W. Carlton, 2007. "Does Antitrust Need to be Modernized?," Journal of Economic Perspectives, American Economic Association, vol. 21(3), pages 155-176, Summer.
    5. Lapo Filistrucchi, 2008. "A SSNIP test for two-sided markets: the case of media," Working Papers 08-34, NET Institute, revised Oct 2008.
    6. John Lopatka, 2011. "Market Definition?," Review of Industrial Organization, Springer;The Industrial Organization Society, vol. 39(1), pages 69-93, August.
    7. Oğuz, Fuat & Akkemik, K. Ali & Göksal, Koray, 2015. "Toward a wider market definition in broadband: The case of Turkey," Utilities Policy, Elsevier, vol. 37(C), pages 111-119.

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