Abstract

http://ssrn.com/abstract=984540
 
 

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Difference in Differences Analysis in Antitrust: What Does it Really Measure?


John Simpson


Federal Trade Commission

David Schmidt


Federal Trade Commission - Antitrust II

May 4, 2007


Abstract:     
Merger retrospectives often use a difference in differences (DID) approach to measure the price effects of mergers. As used in these studies, this approach implicitly assumes that the price in the control market fully controls for supply and demand shocks in the treatment market if the two markets experience the same demand and supply shocks. In this paper, we first show that this is only true if the parameters that determine how supply and demand shocks affect price are the same in the two markets. We then show that in many plausible circumstances the DID approach could either overestimate or underestimate the price effects of a merger.

Number of Pages in PDF File: 10

Keywords: merger retrospectives

JEL Classification: L1,L4,K21

working papers series





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Date posted: May 7, 2007  

Suggested Citation

Simpson, John and Schmidt, David, Difference in Differences Analysis in Antitrust: What Does it Really Measure? (May 4, 2007). Available at SSRN: http://ssrn.com/abstract=984540 or http://dx.doi.org/10.2139/ssrn.984540

Contact Information

John Simpson (Contact Author)
Federal Trade Commission ( email )
601 Pennsylvania Avenue, NW
Washington, DC 20580
United States
David Schmidt
Federal Trade Commission - Antitrust II ( email )
600 Pennsylvania Avenue, NW
Rm 4233
Washington, DC 20580
United States
202-326-2781 (Phone)
202-326-3443 (Fax)
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References:  10
Citations:  1

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