Factor investing explained, value, size, momentum, and quality

The dominant investment philosophy for retail investors over the past 30 years has been total market indexing: own everything, weight by market cap, minimize costs. For most investors, this remains the right approach.

But a body of academic research, much of it from Eugene Fama and Kenneth French at the University of Chicago, has identified specific characteristics that have historically been associated with excess returns above the market beta. These are called factors.

What a factor is

A factor is a systematic characteristic of stocks that has been shown to explain differences in returns across historical data. Unlike stock picking, factor investing doesn't require predicting which individual companies will outperform. It requires owning a basket of stocks that share a characteristic, then maintaining that exposure through diversified holdings.

The major factors

Value: Stocks that are cheap relative to their fundamentals, price-to-earnings, price-to-book, price-to-cash-flow, have historically outperformed growth stocks over long time horizons. The mechanism: the market systematically underprices "boring" companies and overprices exciting ones.

The Fama-French three-factor model (1992) formalized value as a return driver distinct from market beta.

Size (Small-cap premium): Smaller companies have historically outperformed larger ones. The mechanism is partly risk, smaller companies are less liquid, more vulnerable to recessions, and have fewer resources to weather downturns. The premium may be compensation for that risk.

Note: the small-cap premium has been inconsistent in recent decades, particularly in the U.S. The international evidence is stronger.

Momentum: Stocks that have outperformed over the past 6-12 months tend to continue outperforming over the next 3-12 months. The mechanism is behavioral: investor underreaction to good news causes winners to continue winning before the market fully adjusts.

Momentum is the most short-term factor, it requires more frequent rebalancing and generates more taxable events than value or size. In taxable accounts, the after-tax benefit is substantially reduced.

Profitability/Quality: Companies with high operating profitability outperform low-profitability companies. This finding, formalized by Robert Novy-Marx, is sometimes called the quality factor. Profitable companies tend to earn higher future returns than their current valuation would imply.

Low volatility: Counterintuitively, low-volatility stocks have outperformed high-volatility stocks over long periods. The mechanism is behavioral: investors overpay for "exciting" high-volatility stocks and underpay for boring stable ones.

The evidence, and its limitations

Factor premiums are documented across decades of U.S. data and replicated in international markets. This gives them more credibility than most investment strategies.

However:

• Factor premiums have been smaller since publication. Fama and French published their three-factor model in 1992. The value premium in the U.S. has been muted since then, partly because the premium became widely known and was arbitraged, partly because of genuine uncertainty about whether it persists.
• Long periods of underperformance are normal. Value stocks underperformed growth for much of 2010-2020. Maintaining a factor tilt requires accepting years of potential underperformance relative to the total market.
• Factor loading requires tracking error tolerance. A factor-tilted portfolio will look different from the total market in any given year. If you'll abandon the tilt when it lags, you'll lose the benefit of the strategy while incurring the costs.

How to implement factor exposure

Total market + factor tilt: Hold a total market fund as the core (60-80%) and add a value, small-cap, or profitability-tilted fund for the remainder.

Common fund options:

• Vanguard Value ETF (VTV): 0.04%
• iShares MSCI USA Value Factor (VLUE): 0.15%
• Dimensional Fund Advisors (DFA) funds: historically available only through advisors; now available as ETFs (DFAT, DFUV)
• Avantis Investors ETFs: factor-tilted, broadly available (AVUV for U.S. small cap value)

Should you use factors?

For most investors, a total market index is sufficient. The additional complexity of factor tilts is only worth taking on if you:

• Understand the rationale and accept that long periods of underperformance are possible
• Will maintain the tilt through those periods
• Have a long enough time horizon for the premium to potentially materialize
• Keep the factor exposure in tax-advantaged accounts where possible (to avoid the tax drag of rebalancing)

Factors aren't a shortcut or a secret edge. They're a systematic approach that has evidence behind it and requires patience to use correctly.