Factor Investing Explained: Value, Momentum, Profitability, and Size Premiums

A 1993 Paper Changed How We Think About Why Stocks Outperform

Eugene Fama and Kenneth French published "Common Risk Factors in the Returns on Stocks and Bonds" in the Journal of Financial Economics in 1993 — and it rewrote the foundation of investment theory. The paper demonstrated that the simple market beta of the CAPM could not explain observed stock returns: two additional factors — company size (small stocks outperform large) and book-to-market ratio (value stocks outperform growth) — explained a substantial portion of cross-sectional return variation that market beta missed. This wasn't market inefficiency — Fama argued these factors represented compensation for systematic risk. The paper launched a generation of research, eventually identifying five to seven robust factors that have historically delivered premiums above market returns. Factor investing is the practical application of that research — building portfolios that systematically tilt toward these premiums.

The Core Factors: Definitions and Evidence

Academic consensus identifies several factors with robust theoretical foundations and long historical records:

• Market (beta): The original CAPM factor. Stocks outperform cash over long periods, compensating for market risk. Expected premium: 4–6% annually over risk-free rate. The baseline for all other factors.
• Size (SMB — Small Minus Big): Small-cap stocks have historically outperformed large-cap stocks, though the premium is inconsistent and has been weak in recent decades. Theoretical basis: smaller companies are riskier, less liquid, and have higher business failure risk.
• Value (HML — High Minus Low): Stocks with high book-to-market ratios (low price relative to book value, earnings, or sales) have outperformed growth stocks over long periods. Theoretical basis: value companies often face distress risk; the premium compensates for that uncertainty.
• Momentum (WML — Winners Minus Losers): Stocks that have performed well over the past 12 months (excluding the most recent month) tend to continue outperforming over the next 3–12 months. Discovered by Jegadeesh and Titman (1993). Behavioral explanation: investor under-reaction to new information.
• Profitability (RMW — Robust Minus Weak): Companies with high operating profitability outperform low-profitability companies. Added by Fama and French in their 2015 five-factor model. Counterintuitive to some value investors — profitable companies are often not "cheap."
• Investment (CMA — Conservative Minus Aggressive): Companies that invest conservatively (low asset growth) outperform those that invest aggressively. High asset growth often signals overexpansion financed at expensive equity prices.

Historical Factor Premiums (U.S. Data, 1963–2023)

The "Value Is Dead" Debate

Value investing — the strategy most associated with Buffett and Graham, and one of the two original Fama-French factors — experienced a prolonged drought from 2007 to 2020. Growth stocks, particularly U.S. technology companies, dramatically outperformed cheap, high-book-to-market value stocks. This triggered serious academic and practitioner debate:

• Intangibles thesis: Traditional book value accounting understates the value of intellectual property, brand, and human capital — making tech companies appear "expensive" by traditional metrics when they may not be. Researchers like Baruch Lev argued the value factor is broken because accounting has not kept pace with the modern economy.
• Crowding thesis: As factor ETFs attracted hundreds of billions in assets, arbitrage diminished the premium. Too much money chasing the same factor reduced future expected returns.
• Mean reversion thesis: Value's long underperformance created extreme valuation spreads; value staged a significant recovery in 2022 when rising interest rates hurt long-duration growth stocks. Proponents argue the premium is cyclical, not dead.

Factor ETFs: Accessing Premiums at Low Cost

Factor Investing in Practice: What to Expect

Factor premiums are real in historical data — but factor investing requires tolerating extended periods of underperformance relative to the market-cap benchmark:

• The value factor underperformed for more than 12 consecutive years (2007–2020) before recovering strongly
• Momentum delivers strong average returns but experiences catastrophic crashes: momentum lost 73% in the six months following the March 2009 market bottom as losers (which momentum strategies were short) recovered violently
• Small-cap value has been the most consistent factor historically but requires holding through prolonged drawdowns of 40–60% relative to large-cap growth in sustained bull markets

The practical implication: factor investing requires conviction, a long time horizon (10+ years minimum), and the discipline to add exposure during the worst-performing periods — precisely when the behavioral impulse is to abandon the strategy. Investors who chase factor returns after strong performance and sell after weak performance will underperform a simple market index, defeating the purpose entirely.

This article is for informational purposes only and does not constitute financial advice.