On the structure of the set of fixed price equilibria

Working in the framework suggested by Drèze, this paper studies the number of fixed price equilibria and their continuity with respect to the price system. In an exchange economy, the concept of a rationing scheme is introduced, which specifies how shortages are shared among agents. For given utility functions and a given rationing scheme, under standard assumptions, an existence theorem is recalled, and it is shown that the graph of the equilibrium correspondence, when prices and initial endowments vary, is a piecewise continuously differentiable manifold. Moreover, generically, the number of equilibria for an economy, at given prices, is finite and the set of equilibria varies continuously with the price system and the initial endowments.     

Continuous economies with a finite set of equilibria

This paper extends the results of G. Debreu's ‘Economies with a Finite Set of Equilibria’, within the context of the finite dimensional space of economies used therein, to the case where demand functions are assumed only to be continuous and to satisfy a certain technical condition. This condition, involving the concept of approximate limit, does not even require that the function be anywhere differentiable. Our main result is that the complement of the set of economies with a finite set of equilibrium prices has Lebesgue measure zero, although it need not be closed and in fact, may very well be dense.     

The existence of rational expectations equilibria in a large economy with noisy price observations

Non-revealing rational expectations equilibria exist in microeconomic pure exchange economies in which a continuum of uninformed agents have suitably distributed noisy price observations. Slight dispersion in the prices observed by the subset of uninformed consumers is the key condition for continuity (and smoothness) of aggregate excess demand, although individual demands are discontinuous. It leads to equilibria in which markets approximately clear in a strong sense. The equilibria are obtained by applying a fixed point argument to state-dependent excess demand functions.     

On the existence of equilibria in economies with an infinite dimensional commodity space

We prove an infinite dimensional extension of the Gale–Nikaido–Debreu lemma which includes all necessary limiting processes and allows a proof of the existence of equilibria under standard assumptions in an economy with infinitely many commodities which exactly parallels the proof of Debreu (1959) for the finite dimensional case.     

Estimation in threshold autoregressive models with a stationary and a unit root regime

This paper treats estimation in a class of new nonlinear threshold autoregressive models with both a stationary and a unit root regime. Existing literature on nonstationary threshold models has basically focused on models where the nonstationarity can be removed by differencing and/or where the threshold variable is stationary. This is not the case for the process we consider, and nonstandard estimation problems are the result.     

A remark on the existence of equilibria in markets without ordered preferences and with a Riesz space of commodities

We show the existence of competitive equilibria in economies without ordered preferences and a Hausdorff locally convex solid Riesz space of commodities. Our principal assumptions are that the commodity space has a predual and that its positive cone has a non-empty interior.     

A note on the existence of CAPM equilibria with homogeneous cumulative prospect theory preferences

This note identifies and fixes a minor gap in Proposition 1 in Barberis and Huang (Am Econ Rev 98(5):2066–2100, 2008). Assuming homogeneous cumulative prospect theory decision makers, we show that CAPM is a necessary (though not sufficient) condition that must hold in equilibrium. We support our results with numerical examples where security prices become negative.     

On a criterion for the selection of models for stationary time series

Summary A general approach to model selection is described and a criterion for the selection of parametric models for stationary Gaussian time series is derived. A corresponding approximate test is also given and experiences in applying the criterion are reported.     

Matching structure and strategy: Towards a market orientation in health care

The introduction of an ‘internal’ or ‘managed’ market mechanism into the National Health Service required fundamental structural reorganisation, involving the separation of purchaser and provider functions. While a degree of structural change has occurred among the emergent purchasing organisations subsequent to the initial reforms, there is a lack of corresponding evidence of ongoing structural change in acute provider units. Despite the existence of a direct relationship between organisational structure and strategy, the extent of change in the organisational structure of hospitals is questionable. Indeed at the macro level current acute hospital structures, that is NHS Trusts, are remarkably similar to ‘pre-reform’ structures, despite the unsuitability of these structures for the market orientation required by the internal market. Such prevalence arguably reflects the marginal effect that current managerial structures have had on those delivering services and the predominance of the medical hierarchies. Specifically, those responsible for the marketing of hospital services in current structures are not directly linked to those who deliver the service, in spite of the introduction of clinical directorate structures. Part of a broader study of the market behaviour of acute NHS Trusts in Scotland, this paper explores the organisational avenues open to health care providers to overcome this separation in the pursuit of market-led service delivery and concomitant market orientation.     

The substitutes condition and the lattice structure of the set of stable allocations

In the many-to-one matching model with contracts, I show that there is no restriction on preferences weaker than substitutable preferences which guarantees that the set of stable allocations is a lattice. Thus, when contracts are not substitutes, removing agents from the economy may decrease the payoffs to existing agents on both sides of the market.     

Existence and uniqueness of price equilibria: Theory and application to discrete choice models

Continuous excess demand systems which do not obey homogeneity of degree zero or Walras's Law are proved to have equilibria if they satisfy certain mild regularity conditions when prices tend to the extremes of a price domain which need not be closed or bounded. A straightforward generalization of Brouwer's theorem is used. Systems also obeying a weak balance condition (of which Walras's Law is a special case) and homogeneity are treated as corollaries to the main theorem. Sufficient conditions for differentiable excess demand systems to have unique equilibria are developed in three separate theorems. The usefulness of these general existence and uniqueness theorems is demonstrated by applying them to three specific models constructed from discrete choice theory: (1) a competitive rental housing market, (2) a regulated rental housing market with fixed rents and rationing and (3) an interregional labor market in which laborers can choose among regions for employment (or voluntary unemployment) as well as the work hours they will supply.     

Stochastic growth with social-status concern: The existence of a unique stable distribution

This paper extends Kurz’s (1968) growth model to a stochastic growth framework with social-status concern and unbounded production shocks. Using the stochastic monotonicity of a stochastic dynamic system and the methods adopted in Zhang (2007), the existence, uniqueness, and stability of invariant distribution are investigated. Different from the existence of multiple steady states under certainty, it is shown here that there exists a unique stable invariant distribution under uncertainty.     

Generalized extreme value discrete choice demand models : Existence and uniqueness of market equilibria

Generalized extreme value (GEV) random utility choice models have been suggested as a development of the multinomial logit models that allows the random components of various alternatives to be statistically dependent. This paper establishes the existence of and provides necessary and sufficient uniqueness conditions for the solutions to a set of equations that may be interpreted as an equilibrium of an economy, the demand side of which is described by a multiple-segment GEV random choice model. The same equations may alternatively be interpreted in a maximum likelihood estimation context. The method employed is based on optimization theory and may provide a useful computational approach. The uniqueness results suggest a way to introduce segregation/integration effects into logit type choice models. Generalization to non-GEV models are touched upon.     

Assessing the accuracy of the aggregate law of motion in models with heterogeneous agents

This paper shows that the R² and the standard error have fatal flaws and are inadequate accuracy tests. Using data from a Krusell–Smith economy, I show that approximations for the law of motion of aggregate capital, for which the true standard deviation of aggregate capital is up to 14% (119%) higher than the implied value and which are thus clearly inaccurate, can have an R² as high as 0.9999 (0.99). Key in generating a more powerful test is that predictions of the aggregate law of motion are not updated with the aggregated simulated individual data.     

Collusive equilibria with switching costs: The effect of consumer concentration

I study the ability of two competing firms to set collusive prices in markets where consumers have switching costs. In consumer markets (with a small number of consumers), I find an antifolk result in which collusion, in the presence of switching costs, does not arise with patient firms. Patient firms compete aggressively and consumers expect a large utility. A collusive equilibrium is unstable because a deviating firm incorporates the future consumer utility in its deviating price. Also, consumers have a strategic impact so, with the prospects of large utility, they decide to switch to destabilize the firms' collusive agreement. These results do not eventuate in markets with a large number of consumers. In mass markets (a continuum of consumers), a single consumer lacks a strategic impact to destabilize a collusive agreement and a deviating firm cannot appropriate the consumer utility when deviating from collusion. Collusion, then, becomes straightforward to achieve. We show that for any number of consumers, switching costs make collusion easy to sustain.     

Existence of equilibria with infinitely many consumers and infinitely many commodities: A theorem based on models of commodity differentiation

This paper presents a general result on the existence of competitive equilibria in exchange economies in which consumers and commodities are both infinite in number. The result shows that — in this framework at least — the added assumptions necessary to handle models with infinitely many agents are remarkably similar to the additional restrictions needed when only finitely many commodities are available for trade.It is shown that the results apply, in a straightforward manner, to two of the common models of consumer choice when commodity differentiation is an important consideration.