Robert Shimer

The cyclical behavior of equilibrium unemployment and vacancies

This paper argues that the textbook search and matching model cannot generate the observed business-cycle-frequency fluctuations in unemployment and job vacancies in response to shocks of a plausible magnitude. In the United States, the standard deviation of the vacancy-unemployment ratio is almost 20 times as large as the standard deviation of average labor productivity, while the search model predicts that the two variables should have nearly the same volatility. A shock that changes average labor productivity primarily alters the present value of wages, generating only a small movement along a downward-sloping Beveridge curve (unemployment-vacancy locus). A shock to the separation rate generates a counterfactually positive correlation between unemployment and vacancies. In both cases, the model exhibits virtually no propagation.

Assortative Matching and Search

This paper has pushed Beckers matching insights into a quite plausible search setting. Exploiting the implicit integral equation (10), we gave a thorough characterization of cross-sectional matching patterns in the equilibrium and constrained s ocial optimum of a frictional matching model. In so doing, we have developed important new techniques for establishing existence, as well as extended the reach of the supermodularity research program into a wide new arena.

Efficient Unemployment Insurance

This paper constructs a tractable general equilibrium model of search with risk aversion. An increase in risk aversion reduces wages, unemployment, and investment. Unemployment insurance has the opposite effect: insured workers seek high‐wage jobs with high unemployment risk. An economy with risk‐neutral workers achieves maximal output without any unemployment insurance, but an economy with risk‐averse workers requires a positive level of unemployment insurance to maximize output. Therefore, moderate unemployment insurance not only improves risk sharing but also increases output.

Holdups and Efficiency with Search Frictions

A natural holdup problem arises in a market with search frictions: firms have to make a range of investments before finding their employees, and larger investments translate into higher wages. In particular, when wages are determined by ex post bargaining, the equilibrium is always inefficient: recognizing that capital-intensive production relations have to pay higher wages, firms reduce their investments. This can only be prevented by removing all the bargaining power from the workers, but this, in turn, depresses wages below their social product and creates excessive entry of firms. In contrast to this benchmark, we show that efficiency is achieved when firms post wages and workers can direct their search toward more attractive offers. This efficiency result generalizes to an environment with imperfect information where workers only observe a few of the equilibrium wage offers. We show that the underlying reason for efficiency is not wage posting per se, but the ability of workers to direct their search toward more capital-intensive jobs. Copyright 1999 by Economics Department of the University of Pennsylvania and the Osaka University Institute of Social and Economic Research Association.

On-the-Job Search and Strategic Bargaining

This paper studies wage bargaining in a simple economy in which both employed and unemployed workers search for better jobs. The axiomatic Nash bargaining solution and standard strategic bargaining solutions are inapplicable because the set of feasible payoffs is non-convex. I instead develop a strategic model of wage bargaining between a single worker and firm that is applicable to such an environment. I show that if workers and firms are homogeneous, there are market equilibria with a continuous wage distribution in which identical firms bargain to different wages, each of which is a subgame perfect equilibrium of the bargaining game. If firms are heterogeneous, I characterize market equilibria in which more productive firms pay higher wages. I compare the quantitative predictions of this model with Burdett and Mortensen’s (1998) wage posting model and argue that the bargaining model is theoretically more appealing along important dimensions. ∗I am grateful for insightful comments from an anonymous referee and the seminar audience at the Labour Market and Matched Employer-Employee Data conference in Sønderborg, Denmark, especially John Kennan, Dale Mortensen, Eric Smith, and Randall Wright. I also thank the National Science Foundation and the Sloan Foundation for financial support.

Wage and Technology Dispersion

This paper explains why firms with identical opportunities may use different technologies and offer different wages. Our key assumption is that workers must engage in costly search in order to gather information about jobs (Stigler (1961)). In equilibrium, some firms adopt high fixed cost, high productivity technologies, offer high wages, and fill job openings quickly. Other firms adopt less capital-intensive technologies and offer low wages, hiring mostly uninformed workers. In equilibrium, the amount of wage dispersion leaves workers indifferent about whether to gather information, and the fraction of informed workers leaves firms indifferent about their wage and technology choice. We show that worker search, which would appear to be a rent-seeking activity in partial equilibrium, may be efficiency-enhancing in general equilibrium.

SEARCH AND REST UNEMPLOYMENT

This paper extends Lucas and Prescott’s (1974) search model to develop a notion of rest unemployment. The economy consists of a continuum of labor markets, each of which produces a heterogeneous good. There is a constant returns to scale production technology in each labor market, but labor productivity is continually hit by idiosyncratic shocks, inducing the costly reallocation of workers across labor markets. Under some conditions, some workers may be rest-unemployed, waiting for local labor market conditions to improve, rather than engaged in time consuming search. The model has distinct notions of unemployment (moving to a new labor market or waiting for labor market conditions to improve) and inactivity (enjoying leisure while disconnected from the labor market). We obtain closed-form expressions for key aggregate variables and use them to evaluate the model. Quantitatively, we find that in the U.S. economy many more people may be in rest unemployment than in search unemployment.

Matching, Search, and Heterogeneity

This paper explores the efficiency of decentralized search behavior and matching patterns in a model with ex ante heterogeneity and a constant returns to scale search technology. We show that a linear tax or subsidy on search intensity decentralizes the social optimum. In the absence of the tax, high productivity agents are too willing to match, yet they search too little. Low productivity agents have the opposite behavior. As a result, the equilibrium is always inefficient in the absence of taxes, in contrast to known results on the efficiency of decentralized search models with homogeneous agents. We relate the inefficiencies to thick-market and congestion externalities.

On the Optimal Timing of Benefits with Heterogeneous Workers and Human Capital Depreciation

This paper studies the optimal timing of unemployment insurance subsidies in a McCall search model. Risk-averse workers sequentially sample random job opportunities. Our model distinguishes unemployment subsidies from consumption during unemployment by allowing workers to save and borrow freely. When the insurance agency faces a group of homogeneous workers solving stationary search problems, the optimal subsidies are independent of unemployment duration. In contrast, when workers are heterogeneous or when human capital depreciates during the spell, the optimal subsidy is no longer constant. We explore the main determinants of the shape of the optimal subsidy schedule, isolating forces for subsidies to optimally rise or fall with duration.

Stock-flow matching

We develop the implications of the stock-flow matching model for unemployment, vacancies, and worker flows. Workers and jobs are heterogeneous, so most worker-job pairs cannot profitably match, leading to the coexistence of unemployment and vacancies. Productivity shocks cause fluctuations in the number of jobs, which in turn cause fluctuations in other labor market variables. We derive exact expressions for employment and for worker transition rates in a finite economy and analyze their limiting behavior in a large economy. A calibrated version of the model is consistent with the observed co-movement and volatility of labor market variables.