The 1984 justice department guidelines toward horizontal mergers

This paper examines the treatment of economic efficiency in the 1984 revision of the Department of Justice's antitrust Merger Guidelines. An overview of the evolution of the guidelines toward horizontal mergers is presented emphasizing three key areas where changes have occurred. A model is developed following O. Williamson framework is extended to link changes in market concentration (as measured by the Herfindahl-Hirschman Index) that result from a horizontal merger to changes in market power (as measured by price-cost margins). Finally, the cost reductions (economies) required to offset increases in market power are developed in a simulation model. The paper concludes with an application of the model to the LTV-Republic Steel merger.