The Role of Market Definition in Assessing Anti-Competitive Harm in Ohio v. American Express

This article shows that the Supreme Court reached the right outcome in Ohio et al. v. American Express. The District Court had found that American Express was a two-sided transaction platform that provided joint services simultaneously to cardholders and merchants. But it then chose, by adopting a single-sided merchant services market, to analyze the effect of the anti-steering provisions at issue solely on one side of these simultaneous transactions. That decision appears to have prevented the lower court from seeing that the plaintiffs' evidence of anticompetitive harm to merchants was weak. The District Court also decided that case law prevented it from considering the effect of the conduct on the other half of the transactions even at the second-stage of the rule of reason. The Supreme Court did not discuss the limitations of the plaintiffs' theory and evidence at length but simply and properly found that the plaintiffs had failed to prove antitrust injury to platform competition for transactions. This article also shows that criticisms of the Supreme Court decision seem to be based on the rejection or misunderstanding of the economics literature on multi-sided platforms on which the District Court, the Appeals Court, and the Supreme Court all relied