Firms’ principal motives for merging are not to increase market power, but rather to improve firm outcomes through changes in internal operations or structure. Of the 17000+ mergers that occur annually in the U.S., 90% or more have no expectation of an anticompetitive price increase or output reduction. They can profit only by better performance. As a result, the way that we analyze mergers puts the cart before the horse. Rather than using an efficiency “defense” to a prima facie...