The modern portfolio theory pioneered by Markowitz (1952) is widely used in practice and extensively taught to MBAs. However, the estimated Markowitz portfolio rule and most of its extensions not only underperform the naive 1/N rule (that invests equally across N assets) in simulations, but also...

The literature predicts that the average skill level and productivity are higher in larger cities. Prior studies use workers' wage or education differentials to indirectly link city size and output. This article relates city size and productivity directly, using performance data of U.S. equity...