What Is Factor Investing - Decomposing the Sources of Returns
Factor investing is an investment approach that focuses on common characteristics (factors) that explain equity returns, intentionally taking exposure to specific factors. In the 1990s, Eugene Fama and Kenneth French proposed the three-factor model, which demonstrated that in addition to market risk, size (the small-cap premium) and value (the cheap-stock premium) are significant explanatory variables for equity returns. Subsequent research has identified additional factors including momentum (the tendency for past winners to keep winning), quality (the outperformance of high-profitability, low-debt companies), and low volatility (the tendency for less volatile stocks to outperform higher-risk ones).
The core idea behind factor investing is that beyond the overall market return (beta), investors can pursue excess returns (alpha) by tilting toward specific factors. However, factor premiums are not consistently available - each factor can underperform for periods lasting several years. The value factor experienced a prolonged slump in the late 2010s but staged a strong recovery in the 2020s. Practicing factor investing requires understanding this cyclicality and having the patience not to react emotionally to short-term performance.
Characteristics and Interrelationships of Major Factors
The size factor refers to the tendency for smaller companies by market capitalization to outperform larger ones over the long term. Small-cap stocks have greater information asymmetry and less institutional investor coverage, making mispricing more likely - this is considered the source of the premium. The value factor is the tendency for stocks with low price-to-book or price-to-earnings ratios to outperform expensive stocks. The behavioral bias of market participants placing excessive expectations on growth stocks while undervaluing unglamorous cheap stocks is the underlying driver. The momentum factor is the tendency for stocks with high returns over the past 3-12 months to continue performing well, attributed to investors' underreaction to information and herd behavior.
What matters is that correlations between these factors are low, or in some cases negative. books on multi-factor portfolio construction explain that value and momentum often exhibit negative correlation, and combining both can improve the risk-adjusted return of the overall portfolio. Rather than concentrating on a single factor, a multi-factor strategy that combines several factors is the most practical approach for individual investors.
How Individual Investors Can Practice Factor Investing
The easiest way for individual investors to incorporate factor investing is through smart beta ETFs. Numerous ETFs tilted toward specific factors are available, including value ETFs, small-cap ETFs, high-dividend ETFs, and low-volatility ETFs. A satellite strategy that allocates 10-30% of the portfolio to factor ETFs alongside a core index fund offers an excellent balance of cost and risk.
A key caveat when starting factor investing is not to over-rely on backtest results. practical guides to smart beta ETFs also warn that there is no guarantee a factor that worked in historical data will produce the same premium in the future. Understanding the economic rationale behind each factor - whether it represents a risk premium or a behavioral bias - and committing to a long-term perspective is the key to success.
Next Actions to Start Factor Investing
To put factor investing into practice, start by understanding your portfolio's current factor exposures. If you hold a global equity index fund, you already have a large-cap bias due to market-cap weighting. Simply adding 10-20% in small-cap ETFs or value ETFs is a meaningful first step toward factor diversification. A combination of accumulating a global equity fund through the Shin-NISA (Japan's new tax-exempt investment program) tsumitate (regular investment) allocation while purchasing smart beta ETFs through the growth investment allocation is an excellent choice in terms of both cost efficiency and diversification.
The most important thing in factor investing is committing to your chosen strategy for at least 10 years. Just as the value factor experienced a prolonged slump in the late 2010s, every factor goes through periods of underperformance. Abandoning a strategy during short-term underperformance means missing the subsequent recovery. Use a compound interest calculator to see how a factor premium of 1-2% per year compounds into a significant asset difference over 20-30 years, and maintain your motivation for long-term commitment.