Two basic solutions have been proposed to fix the well-documented incompatibility of the sample covariance matrix with Markowitz mean-variance portfolio optimization: first, restrict leverage so much that no short sales are allowed; or, second, linearly shrink the sample covariance matrix towards...

Many researchers seek factors that predict the cross-section of stock returns. The standard methodology sorts stocks according to their factor scores into quantiles and forms a corresponding long-short portfolio. Such a course of action ignores any information on the covariance matrix of stock...

Using a unique proprietary account-level trading dataset in China, we investigate how active information acquisition alleviates price-based return comovement, a typical anomaly in stock splits. We find that: 1) individual trading drives the comovement and the trading correlation between split...