What Structural Presumption? : Reuniting Evidence and Economics on the Role of Market Concentration in Horizontal Merger Analysis

The “structural presumption” is a proposition in antitrust law standing for the typical illegality of mergers that would combine rival firms with large shares of the same market. Courts and commentators are rarely precise in their use of the word “presumption” and there is foundational confusion about what kind of presumption this proposition actually entails. It could either be a substantive factual inference based on economic theory or a procedural device for artificially shifting the burden of production at trial. This Article argues that the substantive inference interpretation is the better reading of case law and the sounder application of the laws of antitrust and evidence. By instead interpreting the structural presumption as a formal rebuttable presumption, modern merger analysis needlessly complicates the use of market concentration evidence and may be systematically undervaluing the probative weight of this evidence. At least in this context, a formal presumption likely confers less evidentiary weight than a simple substantive inference