CHAPTER 2020 Wanting Robustness in Macroeconomics$ Lars Peter Hansen* and Thomas J. Sargent{ * Department of Economics, University of Chicago, Chicago, Illinois.
[email protected] { Department of Economics, New York University and Hoover Institution, Stanford University, Stanford, California.
[email protected] Contents 1. Introduction 1098 1.1 Foundations 1098 2. Knight, Savage, Ellsberg, Gilboa-Schmeidler, and Friedman 1100 2.1 Savage and model misspecification 1100 2.2 Savage and rational expectations 1101 2.3 The Ellsberg paradox 1102 2.4 Multiple priors 1103 2.5 Ellsberg and Friedman 1104 3. Formalizing a Taste for Robustness 1105 3.1 Control with a correct model 1105 3.2 Model misspecification 1106 3.3 Types of misspecifications captured 1107 3.4 Gilboa and Schmeidler again 1109 4. Calibrating a Taste for Robustness 1110 4.1 State evolution 1112 4.2 Classical model detection 1113 4.3 Bayesian model detection 1113 4.3.1 Detection probabilities: An example 1114 4.3.2 Reservations and extensions 1117 5. Learning 1117 5.1 Bayesian models 1118 5.2 Experimentation with specification doubts 1119 5.3 Two risk-sensitivity operators 1119 5.3.1 T1 operator 1119 5.3.2 T2 operator 1120 5.4 A Bellman equation for inducing robust decision rules 1121 5.5 Sudden changes in beliefs 1122 5.6 Adaptive models 1123 5.7 State prediction 1125 $ We thank Ignacio Presno, Robert Tetlow, Franc¸ois Velde, Neng Wang, and Michael Woodford for insightful comments on earlier drafts. Handbook of Monetary Economics, Volume 3B # 2011 Elsevier B.V. ISSN 0169-7218, DOI: 10.1016/S0169-7218(11)03026-7 All rights reserved.