Traditionally, the antitrust agencies have used, among other things, market shares and concentration measures to identify the set of mergers that require further investigation. Market share-based screens have serious limitations, particularly for mergers of firms in differentiated products industries. Calculating and relying on market shares or a market concentration statistic such as the Herfindahl-Hirschman Index requires first defining a relevant market, an exercise well known to be difficult with differentiated products. Moreover, the connection between unilateral effects and market shares is tenuous at best.

In a presentation to the New York Women Antitrust Lawyers Group in New York City on 2 March 2010, NERA Senior Vice Presidents Dr. Christine Meyer and Dr. Lauren Stiroh discussed the use of "upward pricing pressure" as an alternative to market share. Their presentation addressed whether "upward pricing pressure" would provide a useful screening device that the Agencies could use during the initial waiting period to decide whether a Second Request should be issued.