Factor-Based & Multi-Factor Models: Building Systematic Portfolios

Introduction to Factor Investing

Factor investing is a systematic approach to portfolio construction that targets specific drivers of return — known as "factors" — that have been identified through decades of academic research. Rather than selecting individual securities, factor-based strategies select securities based on measurable characteristics (factors) that have historically been associated with excess returns.

This guide presents factor investing concepts for educational purposes. Factor returns are time-varying, and past factor performance does not guarantee future results. Factors can experience prolonged periods of underperformance, and their future persistence is debated among academics and practitioners.

The Fama-French Framework

Three-Factor Model (1993)

Eugene Fama and Kenneth French identified three systematic risk factors that explain the cross-section of stock returns:

• Market (MKT): The excess return of the market over the risk-free rate. This is the traditional CAPM factor.
• Size (SMB — Small Minus Big): Small-cap stocks have historically outperformed large-cap stocks on average.
• Value (HML — High Minus Low): Stocks with high book-to-market ratios (value stocks) have historically outperformed those with low book-to-market ratios (growth stocks).

Five-Factor Model (2015)

Fama and French expanded their model to include two additional factors:

• Profitability (RMW — Robust Minus Weak): Firms with high operating profitability tend to outperform those with low profitability.
• Investment (CMA — Conservative Minus Aggressive): Firms that invest conservatively tend to outperform those that invest aggressively.

Common Factors in Practice

Value Factor

Value investing seeks securities that appear underpriced relative to their fundamentals. Common value metrics include price-to-earnings (P/E), price-to-book (P/B), enterprise value to EBITDA, and free cash flow yield. The value premium has been one of the most debated topics in recent finance, with significant underperformance in the 2010s decade.

Momentum Factor

Securities that have performed well recently tend to continue performing well. The standard momentum factor uses 12-month returns excluding the most recent month (12-1 momentum). Momentum and value factors tend to be negatively correlated, offering diversification potential.

Quality Factor

Quality factors select companies with strong fundamentals: high profitability, stable earnings, low leverage, and strong cash flows. Quality stocks tend to be more resilient during market downturns.

Low Volatility / Minimum Variance

Contrary to traditional finance theory (higher risk = higher return), low-volatility stocks have historically delivered competitive risk-adjusted returns with significantly lower drawdowns.

Multi-Factor Portfolio Construction

Factor Combination Methods

• Intersectional (AND): Select securities that rank highly on multiple factors simultaneously (e.g., cheap AND high momentum). This produces concentrated portfolios with strong factor exposure.
• Union (OR / Composite Score): Create a composite score across factors and select top-ranked securities. This produces more diversified portfolios but with diluted individual factor exposure.
• Sleeve approach: Build separate single-factor portfolios and combine them at the portfolio level. This allows independent factor timing and allocation.

Factor Timing

Some researchers attempt to dynamically adjust factor exposures based on macroeconomic indicators, valuation spreads, or momentum of factor returns. While theoretically appealing, factor timing has proven extremely difficult in practice and remains an active area of academic research.

Implementation Considerations

• Rebalancing frequency: More frequent rebalancing maintains tighter factor exposure but increases transaction costs.
• Turnover management: Factor strategies can have high turnover; buffer rules and patience in trading can reduce costs.
• Capacity constraints: Small-cap and less liquid factor strategies have limited capacity.
• Factor crowding: Popular factors may become crowded, potentially reducing future returns.

Disclaimer: This guide is for educational purposes only. Factor investing involves risks, and factor premiums observed historically may not persist. Past performance of factor strategies does not guarantee future results.