Inconvenient Truths on Merger Retrospective Studies

20 Pages Posted: 7 Jan 2015 Last revised: 25 Mar 2015

See all articles by Gregory J. Werden

Gregory J. Werden

U.S. Department of Justice - Antitrust Division

Date Written: January 5, 2015


Inconvenient truths prevent econometric merger retrospective studies from substantially altering our understanding of competitive effects from horizontal mergers. Econometrics cannot definitively determine the effects of particular mergers, and if they could, econometric merger retrospectives could not provide enough evidence to ground merger assessments in data on actual merger effects rather than in economic theory and legal presumptions. If merger retrospectives are to have some prospect of recalibrating merger enforcement, they must be transformed from econometric exercises into case studies examining the details of the relevant agency’s assessment, but inconvenient truths likely prevent much from being learned through even such studies.

Keywords: antitrust, mergers, merger retrospectives, natural experiments

JEL Classification: L44, K21, L13

Suggested Citation

Werden, Gregory J., Inconvenient Truths on Merger Retrospective Studies (January 5, 2015). 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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