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...

Robert C. Merton is the School of Management Distinguished Professor of Finance at Massachusetts Institute of Technology, and the John and Natty McArthur University Professor Emeritus at Harvard University. Merton received the Alfred Nobel Memorial Prize in Economic Sciences in 1997 for a new...

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...