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This paper introduces time-varying uncertainty into a simple New Keynesian model where the central bank seeks a decision rule that is robust to model misspecification. The paper finds that variation in the central bankXs concern for robustness leads to time-varying, nonnormally distributed impulse responses of output gap, inflation, and the interest rate. These predictions are confirmed by the impulse responses estimated from US quarterly data from 1954 to 2015. Quantitatively, the estimates confirm previous findings that a robust decision maker responds more aggressively than the central bank does empirically.
The standard theory of decision making under uncertainty advises the decision maker to form a statistical model linking outcomes to decisions and then to choose the optimal distribution of outcomes. This assumes that the decision maker trusts the model completely. But what should a decision maker do if the model cannot be trusted? Lars Hansen and Thomas Sargent, two leading macroeconomists, push the field forward as they set about answering this question. They adapt robust control techniques and apply them to economics. By using this theory to let decision makers acknowledge misspecification in economic modeling, the authors develop applications to a variety of problems in dynamic macroeconomics. Technical, rigorous, and self-contained, this book will be useful for macroeconomists who seek to improve the robustness of decision-making processes.
Using stochastic simulations and stability analysis, the paper compares how different monetary rules perform in a moderately nonlinear model with a time-varying nonaccelerating-inflation-rate-of-unemployment (NAIRU). Rules that perform well in linear models but implicitly embody backward-looking measures of real interest rates (such as conventional Taylor rules) or substantial interest rate smoothing perform very poorly in models with moderate nonlinearities, particularly when policymakers tend to make serially correlated errors in estimating the NAIRU. This challenges the practice of evaluating rules within linear models, in which the consequences of responding myopically to significant overheating are extremely unrealistic.
This paper examines monetary policy in Rudebusch and Svensson's (1999) two equation macroeconomic model when the policymaker recognizes that the model is an approximation and is uncertain about the quality of that approximation. It is argued that the minimax approach of robust control provides a general and tractable alternative to the conventional Bayesian decision theoretic approach. Robust control techniques are used to construct robust monetary policies. In most (but not all) cases, these robust policies are more aggressive than the optimal policies absent model uncertainty. The specific robust policies depend strongly on the formation of model uncertainty used, and we make some suggestions about which formulation is most relevant for monetary policy applications.
This thesis consists of three chapters that study the effects of monetary policy uncertainty and deviations from rule-based policy. In the first chapter, I develop an extension of the standard New Keynesian model to monetary policy regime switching to study the impact of uncertainty around the future inflation target. First, I fully characterize how the responses of current inflation and output to inflation target uncertainty depend on the monetary policy rule. If monetary policy is passive, inflation may increase far beyond the anticipated increase in the inflation target, while a strong monetary response to expected inflation results in an immediate drop in the inflation rate. Next, I derive the optimal response of the central bank, which can be achieved by adjusting the current inflation target. A central bank unwilling to adjust the inflation target can optimally adjust other policy rule parameters and can often obtain comparatively similar welfare benefits. Finally, I examine the implications of a perfectly anticipated change in the inflation target and find it is likely to generate cyclical dynamics for inflation and output under a constant policy rule. An optimal time varying policy rule or uncertainty in the period of the inflation target change eliminates cyclical fluctuations and improves welfare. In the second chapter, I apply the New Keynesian model with regime switching of the policy rule to study other dimensions of monetary policy uncertainty. I find that expectations of a regime shift in the future affect current inflation stability in the direction of the expected policy shift, but paradoxically expectations of a shift to a sub-optimal regime may result in better outcomes under the current regime due to the asymmetric effect on output and inflation stability. Additionally, I find that the central bank's first best response is to completely eliminate the uncertainty and that regime switching can only be part of an optimal policy if eventually monetary policy converges to the optimal single regime policy. In the final chapter, I construct the differences between rule-based monetary policy for multiple interest rate rules and the actual interest rates for nine countries using real-time data available to policymakers at the time. I document that more rule-like policy is associated with greater economic stability. Additionally, I find evidence that the association between rule-like policy and greater economic stability is causal by examining the timing of the structural breaks and the changes in central bank policy, using vector autoregressions, and regression specifications relying on the temporal ordering of lagged deviations from the policy rules.
Output gap estimates are subject to a wide range of uncertainty owing to data revisions and the difficulty in distinguishing between cycle and trend in real time. This is important given the central role in monetary policy of assessments of economic activity relative to capacity. We show that country desks tend to overestimate economic slack, especially during recessions, and that uncertainty in initial output gap estimates persists several years. Only a small share of output gap revisions is predictable ex ante based on characteristics like output dynamics, data quality, and policy frameworks. We also show that for a group of Latin American inflation targeters the prescriptions from typical monetary policy rules are subject to large changes due to output gap revisions. These revisions explain a sizable proportion of the deviation of inflation from target, suggesting this information is not accounted for in real-time policy decisions.