Alternatives to the U.S. Antitrust Agency approach to market definition

Shortcomings of the U.S. Antitrust Agency Guidelines method of market definition include failure to focus on competition, the need for cost data, and discontinuities. Two alternative approaches are presented which avoid these problems and the Guidelines' inclusion of substitutes on an all-or-nothing basis. One alternative focuses on the size of a change in capacity of a substitute that would be needed to have the same effects as a unit change in capacity of an initial item. The second proposed alternative offers a simple operational method of giving practical content to the “reasonable interchangeability” concept which is a prominent feature of U.S. Supreme Court decisions. The alternative approaches are evaluated in comparison to that of the Guidelines and some modified versions of the latter.