Glenn Ellison

We examine dynamics in the gender gap in high school mathematics achievement using competition data. A clear gender gap is present by 9th grade, and the gap widens over time. Gender-related differences in dropout rates and in the mean and variance of year-to-year improvement contribute to the widening of the gender gap. The most important difference is that fewer girls make large enough gains to improve their rankings. We also document a discouragement effect: among students falling just short of qualifying for a prestigious second-stage exam, some drop out of future years, and this reaction may be stronger among girls.

We describe the structure and use of epidemiology models of disease transmission, with an emphasis on the susceptible/infected/recovered (SIR) model. We discuss high-profile forecasts of cases and deaths that have been based on these models, what went wrong with the early forecasts, and how they have adapted to the current COVID pandemic. We also offer three distinct areas where economists would be well positioned to contribute to or inform this epidemiology literature: modeling heterogeneity of susceptible populations in various dimensions, accommodating endogeneity of the parameters governing disease spread, and helping to understand the importance of political economy issues in disease suppression.

Technologies, especially the Internet, have transformed how consumers search for products and prices. Price search has become cheap and easy and, therefore, ubiquitous, for many products. Just as technologies have made price search easier, however, they have increased incentives that firms have to obfuscate, or make price search harder. In this article, we focus on these actions that firms take and their effects on market participants. We discuss empirical evidence on this phenomenon, as well as its welfare impacts in the context of theories of search and obfuscation. Finally, we offer a framework for thinking about policy interventions based on this welfare analysis and outline some of the challenges facing policymakers.

We examine the evolution of economics research using a machine-learning-based classification of publications into fields and styles. The changing field distribution of publications would not seem to favor empirical papers. But economics' empirical shift is a within-field phenomenon; even fields that traditionally emphasize theory have gotten more empirical. Empirical work has also come to be more cited than theoretical work. The citation shift is sharpened when citations are weighted by journal importance. Regression analyses of citations per paper show empirical publications reaching citation parity with theoretical publications around 2000. Within fields and journals, however, empirical work is now cited more.

This paper considers a dynamic model of the evolution of open‐source software projects, focusing on the evolution of quality, contributing programmers, and users who contribute customer support to other users. Programmers who have used open‐source software (OSS) are motivated by reciprocal altruism to publish their own improvements. The evolution of the open‐source project depends on the form of the altruistic benefits: in a base case the project grows to a steady‐state size from any initial condition; whereas adding a need for customer support makes zero‐quality a locally absorbing state. We also analyze competition by commercial firms with OSS projects. Optimal pricing policies again vary: in some cases the commercial firm will set low prices when the open‐source project is small; in other cases it mostly waits until the open‐source project has matured.

This article develops models in which obfuscation is individually rational for oligopolistic firms. Firms sell a homogeneous good to rational consumers who incur search costs to learn prices. Search costs are endogenized by allowing obfuscation—firms have an unobservable action that increases the time needed to learn their price. One model involves search costs convex in shopping time. We show that slight convexity can dramatically alter the equilibrium price distribution. A second model examines an informational linkage between current and future search costs: consumers are uncertain about a component of search costs. Here, a signal‐jamming mechanism can lead to equilibrium obfuscation.

We examine the competition between a group of Internet retailers who operate in an environment where a price search engine plays a dominant role. We show that for some products in this environment, the easy price search makes demand tremendously price-sensitive. Retailers, though, engage in obfuscation-practices that frustrate consumer search or make it less damaging to firms-resulting in much less price sensitivity on some other products. We discuss several models of obfuscation and examine its effects on demand and markups empirically. Copyright 2009 The Econometric Society.