Implications of factor-based asset pricing models for estimation of expected returns and for portfolio selection are investigated. In the presence of model mispricing due to a missing risk factor, the mispricing and the residual covariance matrix are linked together. Imposing a strong form of...

We investigate the portfolio choices of mean-variance-optimizing investors who use sample evidence to update prior beliefs centered on either risk-based or characteristic-based pricing models. With dogmatic beliefs in such models and an unconstrained ratio of position size to capital, optimal...

We argue that active management's popularity is not puzzling despite the industry's poor track record. Our explanation features decreasing returns to scale: As the industry's size increases, every manager's ability to outperform passive benchmarks declines. The poor track record occurred before...

We survey the recent literature on learning in financial markets. Our main theme is that many financial market phenomena that appear puzzling at first sight are easier to understand once we recognize that parameters in financial models are uncertain and subject to learning. We discuss phenomena...

We define and study transparency, credibility, and reputation in a model where the central bank's characteristics are unobservable to the private sector and are inferred from the policy outcome. A low-credibility bank optimally conducts a more inflationary policy than a high-credibility bank, in...

Previous analysis of the implementation of inflation targeting is extended to monetary policy responses to different shocks, consequences of model uncertainty, effects of interest rate smoothing and stabilization, a comparison with nominal GDP targeting, and implications of forward-looking...

Inflation targeting is shown to imply inflation forecast targeting: the central bank's inflation forecast becomes an explicit intermediate target. Inflation forecast targeting simplifies both implementation and monitoring of monetary policy. The weight on output stabilization determines how...

Price level targeting (without base drift) and inflation targeting (with base drift) are compared under commitment and discretion, with persistence in unemployment. Price level targeting is often said to imply more short-run inflation variability and thereby more employment variability than...