How far can adding stocks cut a portfolio's risk, and what is the floor that no amount of diversification gets below?
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Worked diversification example at 10% volatility
Compute the covariance and the large- , then sketch against for , and .
Systematic risk versus diversifiable risk
Define systematic (market) risk as the floor the curve settles to after many stocks, and label the gap from single-stock risk as the risk diversification removes.
The minimum-variance boundary
Define the boundary as the least variance available at each expected return, draw it as the left edge of the feasible region, and mark its upper branch.
Long histories and past crises
Record the argument that parameters estimated over long windows already contain episodes such as 1987, 1998 and 2000, and what such estimates leave out.