. Mean dynamics describe the convergence to self-confirming equilibria of selfreferential systems under discounted least squares learning. Escape dynamics recurrently propel away from a self-confirming equilibrium. In a model with a unique self-confirming equilibrium, the escape dynamics make the government discover too strong a version of the natural rate hypothesis. The escape route dynamics cause recurrent outcomes close to the Ramsey (commitment) inflation rate in a model with an adaptive government. Key Words: Self-confirming equilibrium, mean dynamics, escape route, large deviation, natural rate of unemployment, adaptation, experimentation trap. `If an unlikely event occurs, it is very likely to occur in the most likely way.' Michael Harrison 1. INTRODUCTION Building on work by Sims (1988) and Chung (1990), Sargent (1999) showed how a government adaptively fitting an approximating Phillips curve model recurrently sets inflation near the optimal time-inconsistent ouctome, althoug...

We study how decision-makers' concerns about robustness affect prices and quantities in a stochastic growth model. In the model economy, growth rates in technology are altered by infrequent large shocks and continuous small shocks. An investor observes movements in the technology level but cannot perfectly distinguish their sources. Instead the investor solves a signal extraction problem. We depart from most of the macro-economics and finance literature by presuming that the investor treats the specification of technology evolution as an approximation. To promote a decision rule that is robust to model misspecification, an investor acts as if a malevolent player threatens to perturb the actual data-generating process relative to his approximating model. We study how a concern about robustness alters asset prices. We show that the dynamic evolution of the risk-return trade-off is dominated by movements in the growth-state probabilities and that the evolution of the dividend-price ratio is driven primarily by the capital-technology ratio.

. We develop models of robust decision-making and pricing when there are contemporaneous big and small shocks. We illustrate these models using a stochasticgrowth economy. Large shocks are infrequent changes in the technological growth rate, and small shocks are continuous movements in the technology process. Large shocks evolve as a Markov jump process whereas small shocks are a Brownian motion. Robust decision-making is formalized as a two-player game. In contrast to rational expectations agents, our investors are decision-makers who treat models as approximations and fear misspecication. As an algorithmic device to enforce robustness, investors imagine a second, malevolent player, who has the ability to perturb the baseline model. We study two economies, each of which decentralizes a robust resource allocation problem with hidden growth rates. The economies dier in the manner in which the the model is viewed as an approximation. We compare the pricing implications to those that em...

In an economy studied by Lucas and Stokey, tax rates inherit the serial correlation structure of government expenditures, belying Barro's earlier result that taxes should be a random walk for any stochastic process of government expenditures. To recover a version of Barro's random walk tax-smoothing outcome, we modify Lucas and Stokey's economy to permit only risk-free debt. Having only risk-free debt confronts the Ramsey planner with additional constraints on equilibrium allocations beyond one imposed by Lucas and Stokey's assumption of complete markets. The Ramsey outcome blends features of Barro's model with Lucas and Stokey's. In our model, the contemporaneous effects of exogenous government expenditures on the government deficit and taxes resemble those in Lucas and Stokey's model, but incomplete markets put a nearunit root component into government debt and taxes, an outcome like Barro's. However, we show that without ad hoc limits on the government's asset holdings, outcomes can diverge in important ways from Barro's. Our results use and extend recent advances in the consumption-smoothing literature.