Sharpening the Arithmetic of Active Management
挑战了威廉·夏普关于主动管理与被动管理回报相等的著名等式，指出由于市场组合不断变化，主动管理者整体上可以创造正价值，从而在经济中发挥有效配置资源的作用。
I challenge William F. Sharpe’s famous equality that “before costs, the return on the average actively managed dollar will equal the return on the average passively managed dollar.” This equality is based on the implicit assumption that the market portfolio never changes, which does not hold in the real world because new shares are issued, others are repurchased, and indexes are reconstituted—so even “passive” investors must regularly trade. Therefore, active managers can be worth positive fees in aggregate, allowing them to play an important economic role: helping allocate resources efficiently. Passive investing also plays a useful economic role: creating low-cost access to markets.