Selected reading: PDF pages 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23
The chapter develops measures of uncertain returns and explains diversification through the co-movement of holdings. An investment’s contribution to a portfolio depends on more than its own variability.
Return has a distribution
An expected return summarizes possible outcomes and probabilities. Variance and standard deviation describe dispersion around that expectation.
Historical data requires interpretation
The chapter compares long-run asset returns and risk premiums. Those observations have sampling uncertainty and do not directly establish future expected returns.
Co-movement drives diversification
Combining holdings can reduce exposure to company-specific outcomes. Shared market movements limit the risk that adding similar holdings can remove.
Beta asks a portfolio question
Beta measures sensitivity to the market in the stated model and estimation period. It differs from the total standard deviation of an individual holding.