An Index Does Not Carry a Constant Level of Market Risk
Johnson challenges the assumption that passive indexes maintain a stable risk profile. Momentum, constituent changes, and concentration in a handful of large companies can materially increase volatility and make prudent diversification difficult for active managers to beat during a rising market.
- Index risk changes as constituents and weights change
- Concentration can make a broad index less diversified than it appears
- Adding a volatile company can alter the index's risk immediately
- Momentum markets can punish risk-conscious active managers
- Volatility creates more opportunities for active skill to emerge
“there's not enough discussion about how the indexes. The market risk of the index changes”
“the day Tesla was added to the S and P five hundred, it became a much riskier investment”