The stationary sunspot equilibria of a simple overlapping generations economy with heterogeneous agents are considered. These equilibria are known to be suboptimal. The focus of the paper is on the efficacy, based on welfare economic considerations and informational requirements, of government policy in such an environment. The main result is that knowledge of the sunspot equilibrium net trades, weak interval-type information on two parameters, and weak set-type information on the location of some optimal stationary allocation is sufficient to induce a competitive equilibrium that is a Pareto optimal Pareto improvement over the sunspot allocation, which has the further property of reaching a Pareto optimal stationary allocation in finite time. The results are interpreted as demonstrating that, in a simple model with a sunspot environment, policy is very effective and welfare economic considerations lead to stabilization.

We study the impact of a minimum consumption requirement on the rate of economic growth and the evolution of wealth distribution. The requirement introduces a positive dependence between the intertemporal elasticity of substitution and household wealth. This dependence implies a transition phase during which the growth rate of per-capita quantities rise toward their steady-state values and the distributions of wealth, consumption, and permanent income become more unequal. We calibrate the minimum consumption requirement to match estimates available for a sample of Indian villagers and find that these transitional effects are quantitatively significant and depend importantly on the economy's steady-state growth rate.

The behavior of postwar real U.S. GNP, the inputs to an aggregate production function, and several formulations of the associated Solow residuals for the presence of nonlinearities in their generating mechanisms are examined. Three different statistical tests for nonlinearity are implemented: the McLeod-Li test, the BDS test, and the Hinich bicovariance test. We find substantial evidence for nonlinearity in the generating mechanism of real GNP growth but no evidence for nonlinearity in the Solow residuals. We further find that the generating mechanism of the labor input series is nonlinear, whereas that of the capital services input appears to be linear. We therefore conclude that the observed nonlinearity in real output arises from nonlinearities in the labor markets, not from nonlinearities in the technical shocks driving the system. Finally, we investigate the source of the nonlinearities in the labor markets by examining simulated data from a model of the Dutch economy with asymmetric adjustment costs.

We present a method for using rational expectations in a linear-quadratic optimization framework. Following the approach put forward by Sims, we solve the model through a QZ decomposition, which is generally easier to implement than the more widely used Blanchard-Kahn method.

This paper analyzes productive government expenditure in a stochastic AK growth model. First, a centrally planned economy is characterized, emphasizing the trade-off between the effects of both deterministic and stochastic government expenditures on the equilibrium growth rate and its variance. Both the growth-maximizing and the welfare-maximizing shares of government expenditure are derived and shown to depend (differentially) upon the degree of risk in the economy. Whereas production risk reduces the welfare-maximizing share of government expenditure, it may either increase or decrease the growth-maximizing share, depending upon the degree of risk aversion. Next, the stochastic equilibrium in a decentralized economy is derived. The first-best optimal tax structure is characterized and its dependence on risk is determined. The formal analysis is supplemented by some numerical simulations to assess the quantitative significance of risk and the divergence that this generates between the welfare-maximizing and growth-maximizing size of government.

Elhanan Helpman is on a quest for knowledge. He is a researcher in transition, constantly redefining his fields of interest by altering the questions asked and the techniques used. Like many of the great economists, Elhanan has worked in many areas: open economy macro, trade under uncertainty, the new international economics, growth theory, and political economy, to list the most famous. However, this interview is not intended as a review of his contributions. Rather, it is about what drives Elhanan's creative process: his wide-ranging reading, his characteristic stubbornness in tackling problems, the conceptualization of his larger research agenda, and his recollections of how he initiated transitions between fields. It is a very personal interview for those in search of creative inspiration.

Linear dynamical systems are widely used in many different fields from engineering to economics. One simple but important class of such systems is called the single-input transfer function model. Suppose that all variables of the system are sampled for a period using a fixed sample rate. The central issue of this paper is the determination of the smallest sampling rate that will yield a sample that will allow the investigator to identify the discrete-time representation of the system. A critical sampling rate exists that will identify the model. This rate, called the Nyquist rate, is twice the highest frequency component of the system. Sampling at a lower rate will result in an identification problem that is serious. The standard assumptions made about the model and the unobserved innovation errors in the model protect the investigators from the identification problem and resulting biases of undersampling. The critical assumption that is needed to identify an undersampled system is that at least one of the exogenous time series be white noise.