Carl Shapiro and Herbert Hovenkamp ‘Horizontal Mergers, Market Structure, and Burdens of Proof’ (2018) Yale Law Journal 127(7) 1996

This paper, which can be found here, deals with the ‘structural presumption’ for merger control set out in US law by the Philadelphia National Bank case in 1963. In this case, the Supreme Court stated: “That ‘competition is likely to be greatest when there are many sellers, none of which has any significant market share,’ is common ground among most economists, and was undoubtedly a premise of congressional reasoning about the antimerger statute.’ The Supreme Court held that a merger producing a firm that controls an “undue percentage share” of the market and that “results in a significant increase in the concentration of firms in that market” is “inherently likely to lessen competition substantially.” As a result, the merger should be prohibited, at least “in the absence of evidence clearly showing that the merger is not likely to have such anticompetitive effects” The merging parties can then rebut this structural presumption by showing that the market shares do not accurately…