"We analyze the equilibrium size of the active management industry and the role of historical data--how investors use it to decide how much to invest in the industry, and how researchers use it to judge whether the industry's size is reasonable. As the industry's size increases, every manager's...

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...