Everything About Factor Investing: Benefits and Strategies

Updated On: Marzo 19, 2026

Factor Investing has been around for decades and is backed by a vast body of academic research. Yet, it remains widely misunderstood and often debated.

Some myths have persisted for years, while others emerged more recently—especially after the weak performance period between 2018 and 2020, followed by a sharp market shift.

So what is Factor Investing, really?

Where did the idea of factors come from?

And what impact can they have on long-term returns?

In this article, we’ll break down the key concepts of Factor Investing—starting from its definition and origins, all the way to its long-term performance and real-world implications.

Table of Contents

What Is Factor Investing?

To understand the concept behind Factor Investing, it’s necessary to start with some basic financial theory. This means looking at alpha and beta, the CAPM, and the foundational work of Harry Markowitz, William Sharpe, John Lintner, and Jan Mossin.

Not surprisingly, Factor Investing is often referred to as “smart beta.”

William Sharpe, John Lintner, and Jan Mossin developed the Capital Asset Pricing Model (CAPM), which builds on Markowitz’s portfolio theory and introduces the concept of beta.

The CAPM establishes a linear relationship between the systematic risk of a security (measured by beta) and its expected return. Beta measures how sensitive a security’s return is to the overall market return.

CAPM Formula

Where:

E(Ri) = expected return of security i
Rf = risk-free rate
βi = beta of security i
E(Rm) = expected market return
E(Rm) − Rf = market risk premium

Alpha and Beta Explained

The concept of alpha comes from the same theoretical framework that led to the CAPM. It represents the portion of an investment’s return that cannot be explained by beta (systematic risk).

In other words, alpha is the result of idiosyncratic risk.

Put simply, alpha measures a portfolio manager’s ability to generate returns above what would be expected given the level of risk taken:

Positive alpha → outperformance relative to expectations
Negative alpha → underperformance

What Is Beta?

Beta is a measure of the volatility of a security or portfolio relative to the overall market.

It indicates how sensitive an investment is to market movements:

Beta = 1 → the asset moves in line with the market
(If the market rises 10%, the asset also rises ~10%)
Beta > 1 → the asset is more volatile than the market
(If the market rises 10%, the asset may rise ~15%, and vice versa)
Beta < 1 → the asset is less volatile than the market
(If the market rises 10%, the asset may rise ~5%, and vice versa)

From Beta to Smart Beta

Smart beta strategies build on the concept of beta but extend it beyond simple market exposure.

While traditional CAPM beta focuses on how a security moves relative to the overall market, smart beta strategies aim to show that systematic returns can also depend on additional factors.

The goal is to exploit specific factors—such as:

value
size
momentum
quality
minimum volatility

—to construct portfolios that can deliver higher returns or reduce risk compared to traditional benchmarks.

Why It’s Called “Smart Beta”

The term “smart beta” reflects a more advanced and intentional use of the beta concept.

Instead of capturing only market risk, it incorporates multiple drivers of return, applying a more refined and data-driven approach to portfolio construction.

Which Factors Can You Invest In?

Academic research has identified five main factors that investors can target:

Value

The Value strategy aims to generate excess returns by investing in stocks whose market price is lower than their intrinsic value.

This is typically assessed using metrics such as:

price-to-book ratio
price-to-earnings ratio
dividend yield
free cash flow

Size

Historically, portfolios composed of small-cap stocks have delivered higher returns than those focused solely on large-cap companies.

Investors can evaluate size by looking at a company’s market capitalization.

Momentum

Stocks that have performed well in the past tend to continue performing well in the near future.

A momentum strategy typically focuses on relative returns over a period ranging from three months to one year.

Quality

Quality is generally defined by:

low levels of debt
stable earnings
consistent asset growth over time

Investors can identify high-quality stocks using common financial metrics such as:

return on equity (ROE)
debt-to-equity ratio
earnings variability

Minimum Volatility

Empirical research suggests that low-volatility stocks can deliver higher risk-adjusted returns compared to more volatile assets.

A common way to assess this factor is by measuring the standard deviation of returns over a period of one to three years.

Below is the performance of five UCITS accumulating ETFs based on these five factors over the period 2001–2024.

The Impact of Factor Investing on Long-Term Returns

The goal of Factor Investing is to generate higher risk-adjusted returns compared to simple passive investing.

It’s no coincidence that funds tracking factor-based strategies are sometimes described as “semi-active.” The underlying idea is to increase exposure to a more concentrated subset of companies in order to achieve a better return/risk profile.

Factors Focused on Returns

Three of these factors are primarily return-driven:

Momentum
Value
Small Cap (Size)

Small Cap: Investing in Tomorrow’s Giants

The rationale behind investing in smaller-cap companies is to benefit early from the growth of businesses that may become future market leaders.

Today’s giants—such as Amazon, Apple, NVIDIA, and Microsoft—were all small-cap companies 20 or 30 years ago.

They experienced massive valuation growth, but most of that growth occurred during their early expansion phase.

If you had invested through a traditional passive fund tracking the S&P 500 or, even more so, a global equity index, you would have captured only a small portion of that upside. This is because most modern equity indices are market-cap weighted.

👉 The smaller the company, the lower its weight in the index.

The purpose of the Small Cap factor is to accept higher risk—since many small companies may fail or stagnate—in exchange for the chance to identify the next generation of market leaders.

Momentum: Riding the Trend

The Momentum factor aims to generate excess returns in a different way.

It is based on the idea that assets that performed well in the past are likely to continue performing well in the near future.

This concept is closely related to the Lindy effect, which suggests that trends tend to persist over time.

Momentum strategies attempt to benefit from this “inertia effect”:

Companies with strong recent performance are included
Underperforming assets are sold and replaced with better-performing ones

Example of a Factor-Based Portfolio

Here is a simple example of a portfolio incorporating factor strategies, compared to a benchmark like MSCI World Index (SWDA).

⚠️ This is a purely illustrative portfolio, designed to show the potential “spot” impact of factor exposure versus passive investing.
It is not based on rigorous backtesting and should not be implemented without personal evaluation.

Fund	Index	Weight
iShares Core MSCI World UCITS ETF USD (Acc)	MSCI World	70%
Xtrackers MSCI World Momentum Factor UCITS ETF 1C	MSCI World Momentum	10%
SPDR MSCI USA Small Cap Value Weighted UCITS ETF	MSCI USA Small Cap Value Weighted	10%

Criticisms of Factor Investing

Factor Investing is not without its critics.

One notable critique comes from Rick Ferri during his presentation at the Bogleheads Conference 2023.

Ferri, a highly respected financial advisor with extensive industry experience, seven published books, and a Chartered Financial Analyst (CFA) designation, emphasizes the importance of market beta and the dominant role of market trends in driving equity returns.

According to Ferri:

Around 80% of stock returns are explained by overall market movements
Investment factors (size, value, quality, momentum) account for roughly 20% or less

He uses the term “smart beta” to describe the contribution of these factors, but also warns about the illusion of backtesting.

👉 Just because a strategy worked in the past doesn’t mean it will continue to work once it becomes widely known.

This can lead to:

unrealistic expectations
poor investor behavior
increased risk-taking

For this reason, Ferri recommends holding the entire market through index funds, which are generally:

less stressful
more cost-effective
simpler to manage

While he acknowledges the potential benefits of factor investing, he stresses that they are not guaranteed and may involve higher costs and risks.

👉 His practical suggestion: limit factor exposure to no more than 25% of a portfolio, allocating the majority to broad market index funds.

The Backtesting Problem

A similar critique has been raised by Marcos Lopez de Prado in one of his recent publications.

De Prado argues that many studies on Factor Investing are:

outdated
purely associative

According to him, what really matters is establishing a causal relationship between factor exposure and higher expected returns.

Associative vs Causal Studies

Understanding this distinction is crucial.

Associative Studies

These studies identify correlations between variables, without proving cause and effect.

Example:
An observed link between chocolate consumption and heart health does not necessarily mean that chocolate improves heart health.

Causal Studies

These aim to determine whether one variable directly causes changes in another.

They often involve controlled experiments, such as:

giving one group a treatment
giving another group a placebo
comparing the outcomes

This approach allows researchers to isolate true cause-and-effect relationships.

Why Causality Matters in Investing

Causal theories:

allow for more accurate attribution of risk and return
make underlying assumptions more transparent
reduce the likelihood of errors
improve the long-term reliability of investment strategies

De Prado strongly criticizes the financial industry for favoring associative studies, which are:

cheaper
easier to produce
more commercially appealing

However, they may lack true scientific rigor.

The Industry Behind Factor Investing

According to BlackRock, the factor investing industry managed approximately $1.9 trillion in assets in 2017, with projections reaching $3.4 trillion by 2022 (although confirmation of these projections remains unclear).

This highlights a key concern:

👉 A massive industry has been built largely on academic output, rather than consistently proven results for investors.

Bottom Line

Factor Investing offers a structured and research-based approach—but it’s not immune to limitations.

Understanding both its strengths and its criticisms is essential to use it effectively and avoid unrealistic expectations.

Conclusions

As highlighted by a study from AQR Capital Management, the idea behind Factor Investing is rooted in a simple question:

👉 “Who is on the other side of the trade?”

Take value stocks versus expensive stocks as an example.
If everyone decided to overweight cheap stocks and no one was willing to sell them, their prices would rise—meaning they would no longer be cheap.

According to the risk-based view, cheap stocks are undervalued because they are genuinely riskier. They are exposed to risks that many investors are unwilling to تحمل.

As a result:

Investors willing to تحمل that risk earn a return premium
Other investors are willing to “pay” to avoid that risk by favoring more expensive, perceived safer assets

The Key Insight

This leads to a fundamental conclusion:

👉 Factor Investing is, by definition, riskier than passive investing.

By investing in factors, you are deliberately choosing to stand on the other side of the trade, behaving differently from the majority of investors.

Most investors tend to favor more expensive, popular stocks, which leads to: