Following recent evidence of out-of-sample stock market return predictability, the authors aim to evaluate whether the potential benefits suggested by asset allocation theory can actually be captured in the real world using expected return estimates from a predictive system. The question is...

In this paper, we formally show that the cross-sectional variance of stock returns is a consistent and asymptotically efficient estimator for aggregate idiosyncratic volatility. This measure has two key advantages: it is model-free and observable at any frequency. Previous approaches have used...