Title: Essays on Imperfect Competition
Description: The three chapters of my dissertation study imperfect competition, multiproduct firms, and consumer demand. Chapter 1 estimates a structural model of consumer demand and oligopolistic retail competition in order to study three mechanisms through which retailers affect allocative efficiency and consumer welfare. First, variable markups across retail stores within a location induce a misallocation of resources. The deadweight loss from this retail misallocation can be large since a significant fraction of household consumption comes from retail goods. Second, across locations, retail markups may vary with market size. This regional variation plays an important role in recent economic geography models as an agglomeration force. In the limit, models predict that the distortion from variable markups disappears in large markets, although it is an open question, How Large is Large? Third, since retail stores are differentiated, differences in the variety of retail stores available to consumers matters for consumer welfare across locations.

To quantify the importance of these mechanisms, I estimate my model using retail scanner data with prices and sales at the barcode level from thousands of stores across the US. I find that the deadweight loss and consumption misallocation from variable retail markups are economically significant. I estimate that retail markups are smaller in larger cities, and that markets the size of New York City and Los Angeles are approximately at the undistorted monopolistically competitive limit. My results show that retail store variety significantly impacts the cost of living and could be an important consumption-based agglomeration force. The second chapter of my dissertation develops and structurally estimates a model of heterogeneous multiproduct firms that can be used to decompose the firm-size distribution into the contributions of costs, quality, markups, and product scope. In this joint work with Stephen J. Redding and David E. Weinstein, we find that variation in firm quality and product scope explains at least four fifths of the variation in firm sales using Nielsen barcode data on prices and sales.

We show that the imperfect substitutability of products within firms, and the fact that larger firms supply more products than smaller firms, implies that standard productivity measures are not independent of demand system assumptions and probably dramatically understate the relative productivity of the largest firms. Although most firms are well approximated by the monopolistic competition benchmark of constant markups, we find that the largest firms that account for most of aggregate sales depart substantially from this benchmark, and exhibit both variable markups and substantial cannibalization effects. The final chapter of my dissertation develops a new integrable demand system, called the Doubly-Translated CDES demand system, which is well suited to theoretical and empirical work. Commonly used analytically and computationally tractable demand systems severely restrict key properties of demand, which parametrically pins down the answers to many important economic questions. The Doubly-Translated CDES demand system is flexible in important ways that common demand systems are not, while maintaining effective global regularity and global consistency.

Using data, I provide examples of this demand system's flexibility by calibrating different parameter values. I discuss how this demand system can be estimated with regularity imposed and correcting for the endogeneity of prices using constrained Nonlinear GMM.