A recent empirical literature has shaken economists' confidence in the value of aggregate (industry-level) data to illuminate production relationships. But the statistical finding 'you can't aggregate,' however well documented, is not an economic explanation. Plant-level relationships do...

This paper proposes an empirical framework for measuring the effects of entry in concentrated markets. Building on models of entry in atomistically competitive markets, the authors show how the number of producers in an oligopolistic market varies with changes in demand and market competition....