We study the competitive equilibrium of large random economies with linear activities using methods of statistical mechanics. We focus on economies with C commodities, N firms, each running a randomly drawn linear technology, and one consumer. We derive, in the limit N, C ∞ with n=N/C fixed, a complete description of the statistical properties of typical equilibria. We find two regimes, which in the limit of efficient technologies are separated by a phase transition, and argue that endogenous technological change drives the economy close to the critical point.

We examine optimal policy in an open-economy model with uncertainty and learning, where monetary policy actions affect the economy through the real exchange rate channel. Our results show that the degree of caution or activism in optimal policy depends on whether central banks are in coordinated or uncoordinated equilibrium. If central banks coordinate their policy actions then activism is optimal. In contrast, if there is no coordination, caution prevails. In the latter case caution is optimal because it helps central banks to avoid exposing themselves to manipulative actions by other central banks.

We evaluate whether the spirit of capitalism improves the ability of the real business cycle model to explain the main features of both asset return and the business cycle. In our model, the spirit of capitalism is embodied in the assumption that individuals have preferences for financial wealth. Our simulation results suggest that this assumption may improve the model's ability to explain the risk-free rate puzzle but not the equity premium puzzle. This assumption also markedly deteriorates the model's ability to account for the main features of the business cycle.

Over the past two million years human body mass first increased and later declined, peaking about 50,000 years ago. This paper sets up a model of natural selection among body types to explain this pattern. Population, technology, and average body mass evolve endogenously and interdependently in such a way that a takeoff in technological progress generates rising population density and resource depletion. This in turn makes large bodies less useful in food procurement, while keeping their metabolism requirements high. The result is a shift in reproductive advantage from big to small bodies and an endogenous reversal of the time trend in body mass.

In this paper we present and discuss a simple financial accelerator agent-based model, whose conceptual core is the interaction of heterogeneous firms and the banking system. Its simplicity notwithstanding, the model is able to replicate through simulations a large number of stylized facts concerning the shape and evolution over time of the distribution of firms' sizes, growth rates, profits, and “bad debt.”

This paper proposes a simple theory to explain the productivity slowdown observed in Japan during the 1990s. Under a forbearance policy by the government toward nonperforming loans, one keeping insolvent firms afloat, other economic agents become exposed to a higher risk of not being paid by their customers (payment uncertainty). It is shown that the payment uncertainty, working through a competitive market, causes an endogenous decline in the number of firms that are involved in the production of one good. Resulting disruptions of the division of labor among firms lower macroeconomic productivity. The performance of the model is compared with that of the Japanese economy in the 1990s.

We investigate both the rational explosive inflation paths studied by McCallum (2001), and the classification of fiscal and monetary policies proposed by Leeper (1991), for stability under least squares (LS) learning of the rational expectations equilibria (REE). Our first result is that the explosive fiscalist REE is not locally stable under LS learning. In contrast, in Leeper's setting, there are policy regimes for which the fiscalist solution, in which fiscal variables affect the price level, can be a locally stable outcome under LS learning. However, for other policy regimes the monetarist solution is, instead, the locally stable REE.

We consider an economy in which people choose between a random-matching sector and organized markets absent double-coincidence problems. Merchants in the organized markets issue bills of exchange. Pareto-ranked multiple equilibria exist with the extent of the market and circulation of private liabilities endogenously determined. If trade frictions are moderate, bills circulate as a general medium of exchange, and the level of specialization is higher relative to barter. In this case, higher inside liquidity is accompanied by more specialization. When all transactions take place in the organized markets, trading risk vanishes and the economy achieves complete specialization.

Peter Diamond is one of the major contributors to economics during the last half century. His many contributions include research on growth, Social Security, public finance more generally, the economics of uncertainty, search theory, in particular, and economic dynamics, in general. This work has shaped the way we think about many economic problems, and the way in which we formalize them. Among his long list of honors and awards, he is a fellow of the Econometric Society, a Guggenheim Fellow, a Fellow of the American Academy of Arts and Sciences, a Member of the National Academy of Sciences, and a Nemmers Prize winner. The National Science Foundation has supported his work for the last 40 years. A recent check indicated 9 books and 132 published articles, and there are few signs of any slowdown.

We consider a dynamic stochastic model of currency attacks, characterized by imperfect information about a fundamental. Agents not only decide whether to attack the peg but also formulate expectations concerning the probability of future devaluation. The subjective devaluation probabilities influence the inflation expectations, which, in turn, affect the next-period wage level and unemployment. Hence, expectations affect the following-period fundamental and the policymaker's ability to resist an attack. Agents decide upon next-period wage having observed whether the current-period currency attack has been successful or not: this publicly available information is sufficient to allow for a coordination effect among agents, leading to multiple equilibria. Our results imply that a ‘transparent policy’ during a currency crisis is in the policymaker's interest.

We study the constant discount rate present value model for stock pricing in a stochastic setting where the exogenous dividend stream is modeled as a random walk with innovations drawn from the family of stable distributions. We derive an exact analytical solution for the fundamental stock price. We evaluate the ability of the model fundamentals and the dividends-driven intrinsic bubbles to explain the observed variation in annual U.S. stock prices. We compare results obtained in this setting with those from the traditional model where all stochastic processes are driven by Gaussian shocks.

The presumption that R&D is a key driver of economic growth is difficult to reconcile with empirical evidence. For example, in most studies, which identify technical change with total factor productivity (TFP), the link between TFP and measures of knowledge is found to be weak.

This paper shows that a reconciliation may be possible in a model where R&D contributes to growth through investment-specific technical change. Such a model predicts that the empirical link between knowledge and productivty would be weak even if the generation of knowledge is the predominant factor of economic growth. The paper also shows that estimates of the production function for knowledge using patent data may be biased.

Specification tests reject a linear inflation forecasting model over the period 1959–2002. Based on this finding, we evaluate the out-of-sample inflation forecasts of a fully nonparametric model for 1994–2002. Our two main results are that: (i) nonlinear models produce much better forecasts than linear models, and (ii) including money growth in the nonparametric model yields marginal improvements, but including velocity reduces the mean squared forecast error by as much as 40%. A threshold model fits the data well over the full sample, offering an interpretation of our findings. We conclude that it is important to account for both nonlinearity and the behavior of monetary aggregates when forecasting inflation.

Costas Azariadis was born in Athens, Greece, in 1943. He attended the National Technical University in Athens and received a degree in chemical engineering in 1969. He then attended Carnegie Mellon University, receiving an MBA in 1971 and his Ph.D. in 1975. His doctoral dissertation was advised by Edward Prescott and Robert Lucas. Azariadis's first academic appointment was as an assistant professor at Brown University between 1973 and 1977, after which he moved to the University of Pennsylvania. In 1992, he moved to UCLA. In addition, Azariadis spent two semesters at Hebrew University and Princeton and has held briefer visiting positions all over the world.

In various agent-based models, the stylized facts of financial markets (unit roots, fat tails, and volatility clustering) have been shown to emerge from the interactions of agents. However, the complexity of these models often limits their analytical accessibility. In this paper we show that even a very simple model of a financial market with heterogeneous interacting agents is capable of reproducing these ubiquitous statistical properties. The simplicity of our approach permits us to derive some analytical insights using concepts from statistical mechanics. In our model, traders are divided into two groups, fundamentalists and chartists, and their interactions are based on a variant of the herding mechanism introduced by A. Kirman (Ants, rationality, and recruitment, Quarterly Journal of Economics 108, 137–156, 1993). The statistical analysis of simulated data points toward long-term dependence in the autocorrelations of squared and absolute returns and hyperbolic decay in the tail of the distribution of raw returns, both with estimated decay parameters in the same range as those of empirical data. Theoretical analysis, however, excludes the possibility of “true” scaling behavior because of the Markovian nature of the underlying process and the boundedness of returns. The model, therefore, only mimics power law behavior. Similarly to the phenomenological volatility models analyzed by LeBaron (Stochastic volatility as a simple generator of apparent financial power laws and long memory, Quantitative Finance 1, 621–631, 2001), the usual statistical tests are not able to distinguish between true and pseudo-scaling laws in the dynamics of our artificial market.

We consider a model in which foreign and domestic traders buy the assets of both of two countries. Speculators in both countries use chartist or fundamentalist rules for forecasting the exchange rate. Demand for the assets of each country is determined by these forecasts. Perceptions of the fundamentals in each country are not necessarily the same. Rules are used with a certain probability depending on an agent's previous experience with them. The demands of the fundamentalist and chartist agents in the two countries determine the temporary equilibrium exchange rate at each point in time. This is unique under certain assumptions. With traders of both nationalities there is no need, as in other models, for an exogenous supply of foreign exchange. The model produces realistic features of the equilibrium exchange rate series. Periods in which the exchange rate tracks the fundamentals of one of the countries alternate with others in which bubbles appear.

We consider an overlapping generations model with environment and an elastic labor supply. In this framework, consumers have to choose between consumption, environmental quality, and leisure. We show the existence of both deterministic cycles and indeterminacy. In contrast to previous results, the emergence of endogenous fluctuations does not require a high emission rate of pollution.

This paper sets up a two-sector growth model with sectoral hysteresis because of intersectoral factor reallocation costs. The main results are: (i) The economy under study exhibits nonergodic growth implying path-dependency (history matters) and permanent consequences of temporary shocks. (ii) Flexible economies are more likely to take advantage of technological improvements. The analysis points to a new mechanism in the flexibility-growth nexus, which complements the findings of Bertola (1994). (iii) Periods of negative growth can be explained as optimal responses of an economy to favorable technology shocks. This result sheds light on the fact that economic development is associated with recurring downturns.

Our intention is to study, in the framework of a very simple optimal growth model, the consequences on the optimal paths followed by consumption and the environmental quality of an endogenous discounting. Consumption directly comes from the use of environmental services and so is a direct cause of environmental degradation. The environment is valued both as a source of consumption and as an amenity. For a sustainability concern, we introduce an endogenous discount rate growing with the environmental quality, and compare the optimal growth paths with the ones obtained in the usual case of exogenous and constant discounting. We show that the convergence of the environmental quality toward a steady state occurs only for a very special configuration of the parameters in the exogenous discounting case, whereas it occurs generically in the endogenous discounting one. This happens for a utility discount rate becoming sufficiently high when the environmental quality is high and sufficiently low when the environmental quality is poor. In this case, then, endogenous discounting with a positive marginal discount rate allows us to avoid the depletion of the environment.