Guy Laroque

On the Behaviour of Commodity Prices

This paper applies the standard rational expectations competitive storage model to the study of thirteen commodities. It explains the skewness, and the existence of rare but violent explosions in prices, coupled with a high degree of price autocorrelation in more normal times. A central feature of the model is the explicit recognition of the fact that it is impossible for the market as a whole to carry negative inventories, and this introduces an essential non-linearity which carries through into non-linearity of the predicted commodity price series. For most of the thirteen commodity prices, the behaviour of prices from one year to the next conforms to the predictions of the theory about conditional expectations and conditional variances. However, given the non-linearity both of the model and of the actual prices, such conformity is not enough to ensure that the theory yields a complete account of the data. In particular, the analysis does not yield a fully satisfactory explanation for the high autocorrelation observed in the data.

Competitive Storage and Commodity Price Dynamics

By buying cheap and selling dear, risk-neutral commodity speculators can smooth commodity prices and induce serial dependence in price even when none would exist under a simple process of supply and demand. Commodity prices are variable and strongly positively correlated from one year to the next. The variability is often explained by supply factors, and the autocorrelation by the activities of speculators. We show that this explanation is not consistent with the evidence. Speculation can substantially increase autocorrelation for prices that are weakly autocorrelated in its absence, but not to the high levels that are observed in the data.

Using Privileged Information to Manipulate Markets: Insiders, Gurus, and Credibility

Access to private information is shown to generate both the incentives and the ability to manipulate asset markets through strategically distorted announcements. The fact that privileged information is noisy interferes with the publics attempts to learn whether such announcements are honest; it allows opportunistic individuals to manipulate prices repeatedly, without ever being fully found out. This leads us to extend Sobels [1985] model of strategic communication to the case of noisy private signals. Our results show that when truthfulness is not easily verifiable, restrictions on trading by insiders may be needed to preserve the integrity of information embodied in prices.

On temporary Keynesian equilibria

One of the fundamental purposes of Keynesian theory is to present a model of the economy where transactions take place at prices that do not achieve the equilibrium of supply and demand as the classics understood it. This implies that, in such a model, short-run adjustments must take place at least partly by quantity rationing instead of by price movements.

A Model of Commodity Prices after Sir Arthur Lewis

We develop an idea from Arthur Lewis’ paper on unlimited supplies of labor to model the longrun behavior of the prices of primary commodity produced by poor countries. Commodity supply is assumed infinitely elastic in the long run, and the rate of growth of supply responds to the excess of the current price over the long-run supply price. Demand is linked to the level of world income and to the price of the commodity, so that price is stationary around its supply price, and commodity supply and world income are cointegrated. The model is fitted to long-run historical data. D 2003 Elsevier Science B.V. All rights reserved.

Stability of cycles and expectations

The actual dynamics of an economy depends on how agents forecast the future at every date as a function of their information on the past, while possibly learning the structure of their environment. We show in the case of a one-dimensional state variable that under mild conditions on expectations functions, a given cycle with perfect foresight that is stable in the actual dynamics is stable in a fictitious backward perfect foresight dynamics. We exhibit a restricted class of expectations functions for which the converse is true.

Fair allocations in large economies

The purpose of this paper is the study of problems of equity in an economy with many agents. Conditions are given under which every equitable and Pareto optimal allocation is a competitive equilibrium with equal incomes for all agents. The results are also of potential relevance for the literature on incentive compatibility since the allocations that are obained through incentive mechanisms in large economies turn out to be equitable.

Estimation of Multi-market Fix-Price Models: An Application of Pseudo Maximum Likelihood Methods

The past decade has seen the econometric implementation of macroeconomic multimarket fix-price models for a number of European countries. The procedure in use, the full information maximum likelihood method, unfortunately becomes very cumbersome and seems out of reach when additional features are incorporated in the model (disaggregation into micro markets, opinion surveys ...). One purpose of the present work is to prove the fruitfulness of the following estimation strategy: use Monte Carlo simulations to compute the first- and second-order moments of the endogenous variables, and maximize a resulting pseudo likelihood function to estimate the parameters. Copyright 1989 by The Econometric Society.

Social Security and Demographic Shocks

This paper examines the sharing of risks between generations in the framework of an overlapping generations model of social security with shocks to the productivity of labor and capital and demographic shocks. The study focused on stationary long run allocations. The concept of interim optimality was utilized, which amounts to standard Pareto optimality once the state of the world in which the agents are born is known. The set of interim optimal allocations was characterized and the equilibria associated with various institutional forms of social security from the point of view of the optimal criterion were also studied. In addition, the analogs of two traditional welfare theorems of microeconomic theory were obtained.

On competitive cycles in productive economies

Abstract In a model of overlapping generations with production, money, and an endogenous labor supply, general conditions are given for the existence of two different types of cyclical equilibria. The conditions are given in terms of the elasticities of demand for savings and for capital with respect to the interest rate and of the capital-consumption ratio at the golden rule steady state. Examples using CES technologies are also studied.