Andrea Prat, Tommaso Valletti, 26 July 2018

Competition authorities struggle to evaluate the effect of mergers between social media platforms when prices are zero and standard tools like cross-price elasticities are of little use. This column argues that social media platforms are 'attention brokers' that help incumbents maintain market power in other industries by restricting producers’ targeted access to individual consumers. User overlap is more important as a predictor of competition problems than traditional aggregate usage shares. 


CEPR Policy Research