Asset allocation
A map to building factor-based portfolios
November 28, 2023
Investing with a focus on factors—specific equity characteristics such as value, momentum, and quality that drive return and risk—has the potential to enhance market returns over time. An important consideration for investors and advisors pursuing such a strategy is how best to allocate assets in a factor-based portfolio, according to a recent Vanguard research paper, Not all factors are created equal: Factors’ role in asset allocation.
The Vanguard team looks primarily at the mechanics and trade-offs of two factor approaches:
- Market-capitalization weighting, which entails identifying stocks with the desired factor exposure and assigning each stock a portfolio weight based on its relative market cap.
- Signal weighting, which starts with a calculation of the specific factor exposure of a set of stocks and then bases portfolio weight on each stock’s relative exposure to that factor without regard to the stock’s market cap.
"Our paper seeks to educate advisors as well as their clients on the different approaches to factor construction and their trade-offs," said Victor Zhu, CFA, CAIA, one of the paper’s authors.
Two roads diverge in a portfolio
An investor who strongly believes in the value factor may want to achieve a certain target exposure to value in an overall portfolio. After taking their risk appetite, investment objectives, and existing asset allocation into account, the investor could choose either a cap-weighted or a signal-weighted approach to achieve that exposure.
"The way that is the most familiar to investors is market weighting," said Haifeng Wang, Ph.D., CFA, another of the paper’s authors. "For the value factor, if you pick the top one-third of 1,000 stocks with the highest value score—however you define value—and then you use the market cap to weight for those stocks, that’s the market weighting. For signal weighting, we calculate the value score, and we use the score to weight each stock."
That distinction can make a significant difference. For example, as the accompanying graphic shows, an investor starting with a 60% stock/40% bond portfolio would need to allocate 30% of the overall equity assets in a cap-weighted factor fund versus 19% in a signal-weighted factor fund to reach the same targeted value exposure.
Different allocations of cap- and signal-weighted factors can achieve the same exposure
Asset allocations to attain the same factor exposure
Notes: The broad-based market portfolio is represented by the Standard & Poor’s 500 Index.
Sources: Vanguard calculations, based on data from Compustat and Axioma.
The cap-weighted allocation would be expected to deviate less from the broad market but would require a larger capital commitment to achieve a similar factor exposure. The signal-weighted allocation would achieve the same targeted factor exposure more efficiently but would deviate more from broad market returns, adding risk.
Keeping the focus on investor outcomes
The authors argue that factors can be a useful tool for seeking enhanced returns, expressing a directional view on the market, and potentially reducing risk in an investor’s portfolio. Understanding the trade-offs and nuances of different factor approaches may help investors optimize their portfolios and achieve their investment objectives, the authors say.
"Different factors often exhibit low correlations with each other, which means that when one factor is underperforming, another may be outperforming," Zhu said. "This can help reduce the overall risk in a portfolio."
The paper takes an impartial view toward the approaches. "We do not want to make a recommendation for which weighting scheme to use," Wang said. "We just want our readers to be mindful of the risk–return trade-off."
As Zhu put it: "Factor investing is not made for everyone. Depending on one’s investment objective, risk tolerance, horizon, and expertise, a factor fund can be used as a tool to enhance return or diversify real risk, depending on how the investor wants to structure the portfolio."
Related links:
- Striking while the iron’s hot for factor premia (article, issued June 2023)
- Portfolio construction: Principles inform possibilities (article, issued August 2022)
- Vanguard’s portfolio construction framework: From investing principles to custom portfolio solutions (32-page PDF, issued July 2022)
Notes:
All investing is subject to risk, including the possible loss of the money you invest. Diversification does not ensure a profit or protect against a loss. Be aware that fluctuations in the financial markets and other factors may cause declines in the value of your account. There is no guarantee that any particular asset allocation or mix of funds will meet your investment objectives or provide you with a given level of income.
Investments in bonds are subject to interest rate, credit, and inflation risk.
Factor funds are subject to investment style risk, which is the chance that returns from the types of stocks in which a fund invests will trail returns from U.S. stock markets. Factor funds are also subject to manager risk, which is the chance that poor security selection will cause a fund to underperform its relevant benchmark or other funds with a similar investment objective, and sector risk, which is the chance that significant problems will affect a particular sector in which a factor fund invests, or that returns from that sector will trail returns from the overall stock market.
CFA® is a registered trademark owned by CFA Institute.
CAIA® is a registered certification mark owned and administered by the Chartered Alternative Investment Analyst Association.
Contributors

Victor Zhu, CFA, CAIA

Haifeng Wang, Ph.D., CFA