Risk Factor
A systematic, persistent source of risk and return that affects many assets across the market.
What is Risk Factor?
A risk factor is a broad, systematic driver of asset returns and risk that cannot be diversified away by simply holding more securities, because it affects many assets simultaneously. Factor investing rests on the observation that security returns can be explained by exposure to a small number of underlying factors rather than idiosyncratic security selection. The foundational factor is the market factor (beta) from the Capital Asset Pricing Model (CAPM). Fama-French research identified two additional equity factors: size (small-cap stocks have historically outperformed large-cap) and value (cheap stocks by book-to-price have outperformed expensive ones). Subsequent research added momentum, quality (profitability), low volatility, and others. In fixed income, key factors include duration, credit spread, and liquidity. Factor risk premia are theorized to persist because they represent compensation for bearing systematic risk, behavioral biases, or structural market frictions. Investors access factors through smart beta ETFs, factor-tilted funds, and multi-factor strategies.
Example
A portfolio constructed with a tilt toward the value factor (buying stocks trading at low price-to-book ratios) earns a long-run return premium of approximately 3–5% annually above the market factor, according to Fama-French research. In 2020, however, the value factor had one of its worst decades of underperformance — illustrating that factor risk premia are not guaranteed and can go through extended periods of drawdown.
Source: Fama, E. F. & French, K. R. — The Cross-Section of Expected Stock Returns. Journal of Finance, 1992.