Alpha

Alpha originated in the Capital Asset Pricing Model (CAPM), developed in the 1960s by William Sharpe, John Lintner, and Jan Mossin. In CAPM's framework, the expected return of any asset is fully explained by its systematic market risk (beta). Any return in excess of this CAPM prediction is termed 'alpha' — the Greek letter used by Jensen (1968) in his foundational study of mutual fund performance, which is why it is sometimes called 'Jensen's alpha.'

Mathematically, alpha is calculated as the actual portfolio return minus the return that would be expected given the portfolio's beta and the market's performance. If the S&P 500 returned 10% and a fund with a beta of 1.0 returned 13%, the fund generated 3% of alpha. Conversely, if the same fund returned only 8%, it generated -2% of alpha — meaning it underperformed on a risk-adjusted basis despite possibly generating positive absolute returns in a rising market.

Alpha is a cornerstone metric for evaluating active fund managers. The rationale for paying higher fees to an active manager is the expectation that they will generate positive alpha — outperformance that more than compensates for their additional costs. However, decades of academic research have consistently found that the majority of active managers do not generate statistically significant positive alpha over long time periods. After accounting for management fees, transaction costs, and taxes, most actively managed funds underperform their benchmark indices.

This empirical reality has driven the shift toward passive investing. Proponents of the Efficient Market Hypothesis argue that alpha is essentially non-existent after costs because prices already reflect all available information. Practitioners who believe markets are not perfectly efficient — including most hedge fund managers and quantitative traders — continue to seek alpha through proprietary research, algorithmic trading, alternative data sources, and exploitation of behavioral biases among investors.

It is important to distinguish between 'true alpha' — returns attributable to genuine skill or informational edge — and 'factor alpha,' which refers to returns that can be explained by systematic risk factors (such as value, size, or momentum) that happen not to be captured by the benchmark. A manager claiming significant alpha should have their returns evaluated against a multi-factor model, not just a single market index, to verify that the excess return is genuinely unexplained by known risk factors.