Identification in Differentiated Products Markets

Empirical models of differentiated products demand (and often supply) are widely used in industrial organization and other fields of economics. We review some recent work studying identification in a broad class of such models. This work shows that the parametric functional forms and distributional assumptions commonly used for estimation are not essential for identification. Rather, identification relies primarily on the standard requirement that instruments be available for the endogenous variables—here, typically, prices and quantities. We discuss the types of instruments that can suffice, as well as how instrumental variables requirements can be relaxed by the availability of individual-level data or through restrictions on preferences. We also review new results on discrimination between alternative models of oligopoly competition. Together, these results reveal a strong nonparametric foundation for a broad applied literature, provide practical guidance for applied work, and may suggest new approaches to estimation and testing.