The author surveys the statistical evidence on average stock return and the economic theories that try to explain it. The statistical evidence suggests a period of low returns, followed by a slow reversion to a high long-term average. However, that evidence is quite uncertain. Standard economics...

How does traditional portfolio theory adapt to the new facts? The old "two-fund" theorem becomes a "many-fund" theorem; some investors can improve returns by investing in portfolio strategies that let them take on nonmarket sources of risk; and other investors can shed nonmarket risks in the...

In the last 15 years, the cherished "random walk" view that stock returns are unpredictable, the "CAPM" view the market is the only benchmark and market exposure the only source of returns, and the "expectations hypothesis" relating interest rates of various maturities and countries have all...