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Simplifying the Measure of Concentration from Common Ownership: A Note


  • Antonio Estache
  • Maxime Katté
  • Christophe Kieffer


The note presents a simpler alternative to the Modified Herfindahl-Hirschman Index to measure the risks of market concentration in the presence of common owners such as institutional investors owning shares in multiple firms expected to compete in the same market. This new measure, the Amplified Herfindahl-Hirschman Index, delivers the same insights as the MHHI but is less data intensive and less sensitive to outliers. It thus offers a more “user friendly” and more precise alternative to competition and regulatory agencies as a decision trigger for more detailed investigations of market power risks associated with the growing presence of common ownership.

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  • Antonio Estache & Maxime Katté & Christophe Kieffer, 2022. "Simplifying the Measure of Concentration from Common Ownership: A Note," Working Papers ECARES 2022-19, ULB -- Universite Libre de Bruxelles.
  • Handle: RePEc:eca:wpaper:2013/344277

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    References listed on IDEAS

    1. Marie Goppelsroeder & Maarten Pieter Schinkel & Jan Tuinstra, 2008. "Quantifying The Scope For Efficiency Defense In Merger Control: The Werden‐Froeb‐Index," Journal of Industrial Economics, Wiley Blackwell, vol. 56(4), pages 778-808, December.
    2. Bresnahan, Timothy F. & Salop, Steven C., 1986. "Quantifying the competitive effects of production joint ventures," International Journal of Industrial Organization, Elsevier, vol. 4(2), pages 155-175, June.
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    Antitrust; Common Ownership; Institutional Investors; Market Power; Modified Herfindahl-Hirschman Index;
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