We propose a unified model of limited market integration, asset-price determination, leveraging, and contagion. Investors and firms are located on a circle, and access to markets involves participation costs that increase with distance. Due to a complementarity between participation and leverage decisions, the equilibrium may exhibit diverse leverage and participation choices across investors, although investors are ex ante identical. Small changes in market-access costs can cause a change in the type of equilibrium, leading to discontinuous price changes, deleveraging, and portfolio-flow reversals. Moreover, the market is subject to contagion—an adverse shock to investors in some locations affects prices everywhere.

We study the role of communication within a cartel. Our analysis is carried out in Stigler’s (1964) model of repeated oligopoly with secret price cuts. Firms observe neither the prices nor the sales of their rivals. For a fixed discount factor, we identify conditions under which there are equilibria with “cheap talk” that result in near-perfect collusion, whereas all equilibria without such communication are bounded away from this outcome. In our model, communication improves monitoring and leads to higher prices and profits.

Using historical census and survey data, Long and Ferrie (forthcoming) found a significant decline in social mobility in the United States from 1880 to 1973. We present two critiques of the Long-Ferrie study. First, the data quality of the Long-Ferrie study is more limiting than the authors acknowledge. Second, and more critically, they applied a method ill-suited for measuring social mobility of farmers in a comparative study between 1880 and 1973, a period in which the proportion of farmers dramatically declined in the U.S. We show that Long and Ferrie's main conclusion is all driven by this misleading result for farmers.

In 2005–2008, over a dozen put warrants traded in China went so deep out of the money that they were almost certain to expire worthless. Nonetheless, each warrant was traded more than three times each day at substantially inflated prices. This bubble is unique in that the underlying stock prices make warrant fundamentals publicly observable and that warrants have predetermined finite maturities. This sample allows us to examine a set of bubble theories. In particular, our analysis highlights the joint effects of short-sales constraints and heterogeneous beliefs in driving bubbles and confirms several key findings of the experimental bubble literature.

We consider the market design problem of matching students to schools in the presence of crowding effects. These effects are salient in parents’ decision-making and the empirical literature; however, they cause difficulties in the design of satisfactory mechanisms and, as such, are not currently considered. We propose a new framework and an equilibrium notion that accommodates crowding, no-envy, and respect for priorities. The equilibrium has a student-optimal element that induces an incentive-compatible mechanism and is implementable via a novel algorithm. Moreover, analogs of fundamental structural results of the matching literature (the rural hospitals theorem, welfare lattice, etc.) survive.

Child marriage remains common even where female schooling and employment opportunities have grown. We experimentally evaluate a financial incentive to delay marriage alongside a girls' empowerment program in Bangladesh. While girls eligible for two years of incentive are 19 percent less likely to marry underage, the empowerment program failed to decrease adolescent marriage. We show that these results are consistent with a signaling model in which bride type is imperfectly observed but preferred types (socially conservative girls) have lower returns to delaying marriage. Consistent with our theoretical prediction, we observe substantial spillovers of the incentive on untreated nonpreferred types.

Studying job matching in a Kelso-Crawford framework, we consider arbitrary constraints imposed on sets of doctors that a hospital can hire. We characterize all constraints that preserve the substitutes condition (for all revenue functions that satisfy the substitutes condition), a critical condition on hospitals’ revenue functions for well-behaved competitive equilibria. A constraint preserves the substitutes condition if and only if it is a “generalized interval constraint,” which specifies the minimum and maximum numbers of hired doctors, forces some hires, and forbids others. Additionally, “generalized polyhedral constraints” are precisely those that preserve the substitutes condition for all “group separable” revenue functions.

The persistently large number of uninsured, roughly 40 million per year since 1993, continues to elicit bipartisan policy interest. Coverage-expansion proposals without mandates, by far the most common since the defeat of the Clinton plan, must address risk-pooling realities in private markets. Insurers have strong financial incentives to segment risks and minimize pooling of heterogeneous risks, and narrow risk-pooling will diminish the adequacy of premium subsidies based on income alone, at least for higher-risk individuals. The current debate over flat tax credits and the non-group market is a case in point (Blumberg, 2001; Center for Studying Health System Change, 2002; Jack Hadley and James D. Reschovsky, 2002). We, along with nine other teams, were asked to develop a proposal that would expand coverage in a large and creative way (see Holahan et al., 2001). The proposal we developed would subsidize low-income individuals and families but also addresses the issue of inefficient and inequitable risk-pooling.

We introduce a new method to measure the temporal discounting of money. Unlike preceding methods, our method requires neither knowledge nor measurement of utility. It is easier to implement, clearer to subjects, and requires fewer measurements than existing methods.