Jensen's Alpha — The Dollar Dictionary

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Investment

Jensen's Alpha

A risk-adjusted performance measure that calculates how much a portfolio returned above or below what the Capital Asset Pricing Model predicted, given its level of market risk.

Jensen's Alpha was developed by economist Michael Jensen in 1968 as part of his landmark study of mutual fund performance. The formula subtracts the expected return (based on the risk-free rate plus beta times the market premium) from the actual return. What remains is alpha — the value added or destroyed by the manager's active decisions beyond what passive exposure would have delivered.

Persistent positive Jensen's Alpha is extraordinarily rare. Academic research consistently shows that most actively managed funds produce negative alpha after fees — they take on risk, charge fees, and still underperform what a passive index fund at the same risk level would have delivered. The few managers who produce consistent positive alpha (Buffett being the most famous example) are studied intensively because they're the exceptions that prove the rule.

It's the 'did you actually add skill or just take more risk?' test for fund managers. Anyone can beat the market by taking more risk — load up on volatile stocks and you'll occasionally outperform dramatically. Jensen's Alpha strips out the return you'd expect for the risk you took and asks what's left. Positive alpha means genuine skill; negative means you underperformed even after accounting for your risk level.

Real world: A hedge fund that returned 20% in a year might look brilliant — until you calculate that given its beta of 1.8 (taking 80% more market risk than the S&P 500), the CAPM predicted it should have returned 22% in that market environment. The fund's Jensen's Alpha is negative 2% — it actually underperformed its risk-adjusted benchmark despite the impressive absolute number.

💡 Jensen's Alpha is the performance attribution test that separates skill from risk-taking — positive alpha means a manager genuinely added value; negative alpha means they were paid to underperform.

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