Expectational coordination failures and Market outcomes' volatility

The first part of this text reviews the standard economic viewpoint on expectational coordination, a viewpoint that the recent events have challenged. The second part reviews different existing directions assessments of the rational expectations hypothesis that have been made to-date. The third part shows how such a critical assessment, along the lines of the so-called "eductive" learning approach, radically modifies our view of three key problems : the economic role of speculation, the informational efficiency of markets and, last but not least, the ability of agents with long horizon to anticipate the future. The fourth part stresses what has been achieved so far well as the future challenges of the approaches advocated in this paper.expectational coordination ; rational expectations hypothesis

General equilibrium, coordination and multiplicity on spot markets

This is a slightly revised English version of a paper published in the "Revue d'Economie Politique" 112 (5) sept-oct 2002. The text reviews recent work on expectational coordination in general equilibrium models of the Walrasian tradition. It evokes briefly the multiplicity questions associated with infinite horizon models and the issues associated with "eductive learning". It examines in a more systematic way the coordination difficulties that would arise in finite horizon models with spot multiplicity and discusses the relationship between coordination and incompleteness.General equilibrium models ; coordination ; multiplicity

The ECB's New Multi-Country Model for the Euro area: NMCM - with Boundedly Rational Learning Expectations*

Rational expectations has been the dominant way to model expectations, but the literature has quickly moved to a more realistic assumption of boundedly rational learning where agents are assumed to use only a limited set of information to form their expectations. A standard assumption is that agents form expectations by using the correctly specified reduced form model of the economy, the minimal state variable solution (MSV), but they do not know the parameters. However, with medium-sized and large models the closed-form MSV solutions are difficult to attain given the large number of variables that could be included. Therefore, agents base expectations on a misspecified MSV solution. In contrast, we assume agents know the deep parameters of their own optimizing frameworks. However, they are not assumed to know the structure nor the parameterization of the rest of the economy, nor do they know the stochastic processes generating shocks hitting the economy. In addition, agents are assumed to know that the changes (or the growth rates) of fundament variables can be modeled as stationary ARMA(p,q) processes, the exact form of which is not, however, known by agents. This approach avoids the complexities of dealing with a potential vast multitude of alternative mis-specified MSVs. Using a new Multi-country Euro area Model with Boundedly Estimated Rationality we show this approach is compatible with the same limited information assumption that was used in deriving and estimating the behavioral equations of different optimizing agents. We find that there are strong differences in the adjustment path to the shocks to the economy when agent form expectations using our learning approach compared to expectations formed under the assumption of strong rationality. Furthermore, we find that some variation in expansionary fiscal policy in periods of downturns compared to boom periods.

Learning and Endogenous Business Cycles in a Standard Growth Model

Cyclical or chaotic competitive equilibria that do not exist under perfect foresight are shown to occur in a decentralized growth model under constant gain adaptive learning. This paper considers an economy populated by boundedly rational households making one-period ahead constant gain adaptive input price forecasts, and using simple expectation rules to predict long-run physical capital holdings and consumption. Under these hypotheses, lifetime decisions are derived as time unfolds, and analytical solutions to the representative household's problem exist for a standard class of preferences. Under various characteristics of the model's functional forms, competitive equilibrium trajectories under learning may exhibit opposite local stability properties depending whether the underlying information set accommodates all contemporary data. Calibrated to the U.S. economy, the model with boundedly rational households may exhibit endogenous business cycles around the permanent regime which is a saddle point under perfect foresightbounded rationality, constant gain adaptive learning, endogenous business cycles

The ECB's New Multi-Country Model for the euro area: NMCM - with boundedly rational learning expectations

Rational expectations has been the dominant way to model expectations, but the literature has quickly moved to a more realistic assumption of boundedly rational learning where agents are assumed to use only a limited set of information to form their expectations. A standard assumption is that agents form expectations by using the correctly specified reduced form model of the economy, the minimal state variable solution (MSV), but they do not know the parameters. However, with medium-sized and large models the closed-form MSV solutions are difficult to attain given the large number of variables that could be included. Therefore, agents base expectations on a misspecified MSV solution. In contrast, we assume agents know the deep parameters of their own optimising frameworks. However, they are not assumed to know the structure nor the parameterisation of the rest of the economy, nor do they know the stochastic processes generating shocks hitting the economy. In addition, agents are assumed to know that the changes (or the growth rates) of fundament variables can be modelled as stationary ARMA (p,q) processes, the exact form of which is not, however, known by agents. This approach avoids the complexities of dealing with a potential vast multitude of alternative mis-specified MSVs. Using a new Multi-country Euro area Model with Boundedly Estimated Rationality we show this approach is compatible with the same limited information assumption that was used in deriving and estimating the behavioral equations of different optimizing agents. We find that there are strong differences in the adjustment path to the shocks to the economy when agent form expectations using our learning approach compared to expectations formed under the assumption of strong rationality. Furthermore, we find that some variation in expansionary fiscal policy in periods of downturns compared to boom periods. JEL Classification: C51, D83, D84, E17, E32bounded rationality, Expectation, heterogeneity, imperfect information, Learning, macro modelling, open-economy macroeconomics

Adaptive Rational Equilibrium with Forward Looking Agents, fortcoming in International Journal of Economic Theory (IJET) 2006, special issue in honor of Jean-Michel Grandmont.

Brock and Hommes (1997) introduce the concept of adaptive rational equilibrium dynamics (ARED)}, where agents choose between a costly rational expectation forecast and a cheap naive forecast, and the fractions using each of the two strategies evolve over time and are endogenously coupled to the market equilibrium price dynamics. In their setting agents are backward looking in the sense that strategy selection is based on experience measured by relative past realized profits. When the selection pressure to switch to the more profitable strategy is high, instability and complicated chaotic price fluctuations arise. In this paper we investigate the ARED with \textit{forward looking} agents, whose strategy selection is based upon expected profits. Our findings suggest that forward looking behavior dampens the amplitude of price fluctuations, but local instability of the steady state remains. The global dynamics depends upon how sophisticated the forward looking behavior is. With perfectly forward looking agents prices converge to a stable 2-cycle, while with forward looking agents who are boundedly rational concerning their estimate of expected profits, small amplitude chaotic price fluctuations may arise. We also establish an equivalence relationship between a heterogeneous agent model with switching of strategies and a representative agent framework, where the representative agent optimally chooses between the benefits of a high quality forecasts and the associated information gathering costs. To an outside observer it is impossible to distinguish between the two.

Nonlinearity and chaos in economic models: implications for policy decisions

This survey paper discusses the policy implications that can be expected from the recent research on nonlinearity and chaos in economic models. Expected policy implications are interpreted as a driving force behind the recent proliferation of research in this area. In general, it appears that no new justification for policy intervention is developed in models of endogenous fluctuations, although this conclusion depends in part on the definition of equilibrium. When justified, however, policy tends to be very effective in these models.Macroeconomics ; Economic stabilization

Selection in asset markets: the good, the bad, and the unknown

In this paper, we use a series of simple examples to illustrate how wealth-driven selection works in a market for Arrow securities. Our analysis delivers both a good and a bad message. The good message is that, when traders invest constant fractions of their wealth in each asset and have equal consumption rates, markets are informationally effcient: the best informed agent is rewarded and asset prices eventually reflect this information. However, and this is the bad message, when asset demands are not constant fractions of wealth but dependent upon prices, markets might behave suboptimally. In this case, asymptotic prices depend on preferences and beliefs of the whole ecology of traders and do not, in general, reflect the best available information. We show that the key difference between the two cases lies in the local, i.e. price dependent, versus global nature of wealth-driven selection.Market Selection; Evolutionary Finance;Informational Efficiency; Asset Pricing; CRRA Preferences