We examine horizontal mergers amongst Part D insurers with the aim of decomposing market power, cost efficiency, and bargaining power effects. We apply a differences-in-differences identification strategy to panel data on plans offered between 2006 and 2012 to analyze the effects of mergers on...

A growing body of literature analyzing the distributive consequences of regulation suggests that regulation may have particularly detrimental effects on lower income households. Regulation can be regressive if it represents the preferences of the wealthy while imposing costs on all households....