The structural presumption in the 2023 US Merger Guidelines

The Trump Administration has signaled its intention to continue reliance on the 2023 US Merger Guidelines. One important change in the Guidelines relative to their 2010 predecessor is the switch to a stronger structural presumption of anti-competitive harm. In this paper, we evaluate whether the new structural presumption improves the ability of US antitrust agencies to distinguish anti-competitive and benign mergers. Using simulated merger data, we find that the 2023 Guidelines may significantly increase the number of mergers flagged for review, reducing the false-negative rate but dramatically raising the false-positive rate. Alternative presumptions based solely on changes in the Herfindahl–Hirschman Index may outperform the 2023 Guidelines in detecting unilateral price effects. We also show that a stricter structural presumption does not appear to enhance the detection of coordinated effects.