Assessing Market Power: The Trade-off Between Market Concentration and Multi-Market Participation

This analysis reveals that traditional market power measuresare biased under the conditions of multi-market participationand demand interdependence. Specifically, when complementary(substitutable) demands dominate, traditional market power measuresare biased upward (downward). A similar bias carries over tothe evaluation of mergers. To wit, mergers that simultaneouslyincrease market concentration and multi-market participationcan result in lower prices even in the absence of merger economies.It follows that merger guidelines that place undue emphasison market concentration can lead policymakers to block (approve)mergers that enhance (diminish) consumer welfare.