Is there a Perfect Portfolio for investors?
We posed this question to 10 of the most respected pioneers in the investment community. Six have Nobel Prizes in Economics: Harry Markowitz, the founder of Modern Portfolio Theory, the basis of the modern investment portfolio; his protégé William Sharpe, creator of the Capital Asset Pricing Model (CAPM) and the beta risk measure that changed how we think about risk and reward in the financial markets; Eugene Fama, who developed the Efficient Market Hypothesis; Myron Scholes and Robert Merton, two of the co-creators of the Black-Scholes/Merton option pricing model; and Robert Shiller, the behavioral economist whose work challenged the notion of market efficiency.
The other four are portfolio managers, investors and bestselling authors who have sold millions of investment books, including The Vanguard Group’s founder Jack Bogle; the “Bond Guru,” Marty Leibowitz; the “Wisest Man on Wall Street” and Greenwich Associates founder Charles Ellis; and the “Wizard of Wharton,” Jeremy Siegel.
It’s no surprise that there isn’t consensus among their suggestions, given their varied backgrounds and interests. The different viewpoints of these financial luminaries illustrate the complexity of portfolio management—one size clearly doesn’t fit all.
Think of the Perfect Portfolios of our experts as building blocks for your own Perfect Portfolio, collectively capable of accommodating the goals and constraints of all investors, if used in the right combination.
Markowitz suggests that first and foremost, you should diversify. Focus only on portfolios of securities, and in particular, those that have the highest level of expected returns for a given level of risk, Markowitz’s famous efficient frontier. The same concept applies across asset classes like bonds, real estate and commodities. The key for the investor is to find securities and asset classes with low correlations to each other, so that movements in one are not necessarily reflected in the others.
Sharpe’s Perfect Portfolio is just what his famous Capital Asset Pricing Model suggests: investing in the market as a whole. Sharpe recommends a U.S. total stock market fund, a non-U.S. total stock market fund, a U.S. total bond market fund, and a non-U.S. total bond market fund.
Read: A Boglehead explains the simplest way to manage your money
Fama and his collaborator Ken French created a model that starts with Sharpe’s CAPM and augments it with two other factors. One captures the difference in returns between value and growth stocks, while the other captures the difference between stocks in companies with small and large market capitalizations. Fama suggests tilting your diversified portfolio toward value stocks and small-cap stocks, both of which tend to do well over time.
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As the creator of the first index mutual fund, Bogle’s portfolio was all about stock and bond index funds, such as Vanguard’s ETF that tracks the S&P 500 index SPX,
For Scholes, the Perfect Portfolio is about risk management. Your investment success will depend most on avoiding the downside “tail risks,” rare but severe stock market downturns such as the financial crisis of 2007–2009 or the COVID-19 pandemic, while capitalizing on the positive “tail gains.”
Pay attention to what the derivatives markets such as the VIX volatility index VIX,
For Merton, ultimately, the Perfect Portfolio should be your very own risk-free asset, like the inflation-protected government bond TIPS. For your retirement goal, ideally you would take your savings at retirement, and buy an annuity that would provide a lifetime income to meet your anticipated needs.
Leibowitz’s Perfect Portfolio is about the amount of risk you can personally bear. Be prepared to try to make some tough judgment calls, and consider all of your circumstances, including potential life events, current taxes and estate taxes. In addition to equities, you should include bonds to reduce its overall volatility. Have a contingency plan to deal with serious adverse events.
For Shiller, your Perfect Portfolio should be widely diversified, not only across major asset classes, but internationally as well. Place a heavier than typical weight in stocks around the world, where Shiller’s CAPE ratios—that is, cyclically adjusted price-to-earnings ratios—are relatively low.
For Ellis, one of the original advocates of passive investing, your Perfect Portfolio should of course include index funds, especially if you want to have a good chance of being in the top 20% of funds over the next 20 years. You should invest in bond index funds and low-cost international index funds, such as the MSCI EAFE (Europe, Australasia, and Far East) index. Pay attention to your taxes.
And Siegel encourages you to have reasonable expectations in line with financial history, no surprise for the author of the bestselling “Stocks for the Long Run”. The longer your investment horizon, the greater proportion of your Perfect Portfolio should be in stocks. Consider developing-country stocks. For fixed-income investments, consider TIPS.
Finally, as you build your Perfect Portfolio, reflect on your degree of risk aversion, your earning power, the magnitude of your current and future desired wealth, and the magnitude of your current and future financial needs. To assist you, we have created a four-question survey to help you discover where you fit in among 16 types of investors. It then points you toward your Perfect Portfolio and an action that may help you achieve it.
Andrew W. Lo and Stephen R. Foerster are co-authors of “In Pursuit of the Perfect Portfolio: The Stories, Voices, and Key Insights of the Pioneers Who Shaped the Way We Invest”.
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