Essays on model uncertainty in macroeconomics

My dissertation grapples with the issues of model uncertainty in macroeconomics, and analyzes its consequences for monetary policy. It consists of three essays.; In the first essay (Chapter 1), "Monetary Policy under Misspecified Expectations", I examine policy choices for the central bank that faces uncertainty about the process of expectation formation by economic agents. The economy contains both "rule-of-thumb" agents who base their expectations on recent observations and agents who have rational expectations. The central bank is uncertain about the fraction of the rule-of-thumb agents. This uncertainty concern enables me to partially rationalize the over cautious policy stance of the Fed: empirically observed policy in the past two decades involves much weaker responses than optimal policies derived from various micro-founded models. It is well understood that when the economy is more forward-looking, the central bank displays more aggressive responses to inflation and output. But the uncertainty-averse central bank evaluates policies by the performance in the worst case. In my economy this has a high fraction of agents that are backward-looking. The best policy the central bank chooses thus involves moderate responses. That is to say, this minimax policy moves closer toward actual less responsive policy.; In the second essay (Chapter 2), "Phillips Curve Uncertainty and Monetary Policy", I investigate the effect of model uncertainty on policy choices employing a more general approach, which nests the minimax and Bayesian approaches as limiting cases. The central bank is uncertain about whether the economy has a sticky price Phillips curve or a sticky information Phillips curve. I argue that how the central bank chooses a policy depends both on its perception of uncertainty environment and on its attitude towards uncertainty. I find that as the central bank either becomes more uncertainty-averse or considers sticky information more plausible, the response to inflation decreases and to output increases.; The third essay (Chapter 3) is entitled "Optimal Simple Rules in RE Models with Risk Sensitive Preferences". This paper provides a useful method to solve optimal simple rules under risk sensitive preference in macro models with forward looking behavior. An application to a new Keynesian model with lagged dynamics is offered and risk sensitive preference is found to amplify policy responses.