Should DOJ’s Controversial Approach to Market Definition Control Merger Litigation, the Case of US v. H&R Block

35 Pages Posted: 27 Feb 2013 Last revised: 24 Oct 2013

See all articles by Joseph J. Simons

Joseph J. Simons

Paul, Weiss, Rifkind, Wharton & Garrison LLP

Malcolm B. Coate


Date Written: October 24, 2013


Sometimes what appears to be a little, almost imperceptible change can have a huge impact on a policy regime. The recently revised DOJ/FTC Horizontal Merger Guidelines contain such a change, as the document recognizes the importance of Critical Loss Analysis in defining a market, but introduces a theoretical construct to control the analysis. This approach imposes a structure based on the economist’s Lerner index, and then applies a specific style of diversion analysis to compute the actual loss to a hypothetical price increase. We show that this methodology almost guarantees narrow markets, a change that could support a very significant increase in the level of merger enforcement. However, we also show how this aggressive policy result depends on specific assumptions that are often not justified. Change these assumptions and the traditional implications of a critical loss analysis are restored. The recent Department of Justice (DOJ) challenge of H&R Block’s proposed acquisition of the TaxACT software is used to illustrate the problem. Unjustified theoretical assumptions allowed the DOJ’s expert economist to testify to a narrow market that virtually guaranteed that the merger would be found anticompetitive. In effect, theory, if allowed to control market definition analysis, would significantly reduce the plaintiff’s burden of proof and expand the potential for merger enforcement.

Keywords: market definition, critical loss, diversion, H&R Block, Merger Guidelines

JEL Classification: K21, L40

Suggested Citation

Simons, Joseph J. and Coate, Malcolm B., Should DOJ’s Controversial Approach to Market Definition Control Merger Litigation, the Case of US v. H&R Block (October 24, 2013). Available at SSRN: or

Joseph J. Simons (Contact Author)

Paul, Weiss, Rifkind, Wharton & Garrison LLP ( email )

New York, NY 10019
United States

Malcolm B. Coate

Independent ( email )

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