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Alpha and beta decomposition is the process of separating a portfolio's return into the portion explained by market exposure (beta) and the portion representing genuine skill or factor tilts (alpha). This decomposition is fundamental to performance evaluation because it prevents an investor from confusing market returns with skillful investing. A fund that returns 20% in a year when the market rises 25% has not demonstrated skill; it has simply delivered high beta with negative alpha.
In the CAPM framework, beta is the slope coefficient from regressing a portfolio's excess returns against the market's excess returns. A beta of 1.2 means the portfolio is expected to move 1.2% for every 1% move in the market. Alpha is the intercept of this regression, representing the average return not explained by market exposure. The CAPM defines alpha as the "skill" component, but in practice, apparent CAPM alpha may simply reflect exposures to other priced factors like value, momentum, or quality.
Multi-factor alpha is measured by regressing portfolio returns against multiple factor returns simultaneously. The Fama-French-Carhart four-factor model is the standard: Market, SMB (small minus big), HML (high minus low book-to-market), and MOM (momentum). Alpha in this framework represents the return not explained by any of these systematic factors. If a manager claims to generate alpha but their returns are fully explained by a combination of value and momentum tilts, they are delivering factor exposure, not alpha, and the investor could replicate those returns more cheaply with factor ETFs.
Jensen's alpha, which is the CAPM intercept, and multi-factor alpha are both annualized and expressed as a percentage. The statistical significance of alpha should be evaluated using the t-statistic. An alpha of 2% per year with a t-statistic of 0.5 is not meaningfully different from zero. Rules of thumb suggest that alpha is reliable when the t-statistic exceeds 2.0, which requires either a large alpha, low residual volatility, or a long track record.
Portable alpha strategies attempt to separate alpha generation from beta exposure. The investor generates alpha from one source (such as a long-short equity strategy) and obtains beta exposure from another (such as index futures). This allows the investor to deploy alpha-generating skill on top of any desired market exposure. For example, a pension fund might maintain full equity market exposure via futures while allocating its physical capital to a market-neutral hedge fund, effectively "porting" the hedge fund's alpha onto the equity beta.