Common questions about Modern Portfolio Theory (MPT)

QuietGrowth - Common questions about Modern Portfolio Theory (MPT)

We hope to provide a clearer understanding of Modern Portfolio Theory by answering common questions.

1. Does MPT consider taxes and transaction costs?

In its purest form, MPT does not consider taxes or transaction costs, as it assumes a world of frictionless trading. However, these factors can significantly impact investment returns when applied in the real world. Therefore, many portfolio managers that use MPT principles also incorporate strategies to manage taxes and minimise transaction costs. This might involve favouring investments that offer favourable tax treatment, such as tax-efficient funds or tax-exempt bonds, within the context of an optimal portfolio.

2. How does MPT handle changing market conditions?

MPT uses historical data to estimate future risk and returns, which can be a limitation in rapidly changing market conditions. However, it also supports adjusting the portfolio to changing market dynamics. Some advanced portfolio optimisation methods also allow for changing correlations and volatilities, offering a more realistic model of market behaviour.

3. How relevant is MPT in today’s globalised economy?

MPT remains highly relevant in today’s globalised economy. The ability to diversify across different asset types, including international investments, aligns well with the principles of MPT. Moreover, MPT provides a systematic way to manage risk and optimise returns in a complex, interconnected global financial market.

4. Can MPT protect investors from market crashes?

MPT helps manage and mitigate risk, but it doesn’t eliminate it. During a market crash, most assets tend to fall in value, and a portfolio based on MPT principles is not immune to this. However, through diversification, it aims to limit the potential losses.

5. How often should portfolios be rebalanced in MPT?

The rebalancing frequency can depend on several factors, including market conditions, transaction costs, and specific changes in the portfolio’s asset allocation. Some financial advisers suggest a time-based schedule (such as quarterly or annually), while others recommend rebalancing whenever the portfolio’s allocation drifts considerably from its target.

6. Can MPT help in asset allocation for retirement planning?

Yes, MPT can be a valuable tool for retirement planning. It can guide the asset allocation process, enabling investors to build a portfolio that aligns with their risk tolerance, return objectives, and investment horizon. Then, as investors near retirement, they might adjust their portfolios to reduce risk in line with MPT principles.

7. How are correlations between assets considered in MPT?

Correlation coefficients measure the degree to which two assets move with each other and play a key role in MPT. If two assets are perfectly positively correlated (correlation coefficient of +1), they would move exactly in tandem and offer no diversification benefits. On the other hand, if two assets are perfectly negatively-correlated (correlation coefficient of -1), one would rise when the other falls, offering substantial diversification benefits. Realistically, most assets have a correlation coefficient between -1 and +1, and MPT helps identify the optimal mix of assets to minimise risk based on these correlations.

8. Does MPT consider the impact of inflation?

In its basic form, MPT does not directly account for inflation. However, inflation can affect the expected returns of assets and should be considered when building and managing a portfolio. In practice, investors can adjust their expected return rates to account for the expected inflation rate, effectively working with ‘real’ return rates rather than ‘nominal’ return rates.

9. Does MPT work for socially responsible or impact investing?

Yes, MPT can work for socially responsible, ethical or impact investing. In this case, the universe of potential investments would be limited to those that meet the investor’s ethical or impact criteria. Within this universe, the principles of MPT can be applied to select a diversified portfolio that optimises the trade-off between risk and return based on the investor’s preferences.

10. How does MPT treat investments in real estate?

Real estate can be a part of an investment portfolio, offering the potential for both income and capital appreciation. In MPT, real estate investments would be treated like any other asset, with their expected returns, risk, and correlations with other assets considered when constructing the portfolio. The diversification benefits of real estate can potentially enhance a portfolio’s risk-return profile, according to MPT.

11. How does MPT handle investments in different currencies?

When investing internationally, changes in exchange rates can affect the returns of investments denominated in foreign currencies. In MPT, these currency risks can be incorporated into the risk and return estimates for the relevant assets. Currency hedging strategies can also be used to manage this risk. International investments can provide additional opportunities for diversification, a core principle of MPT.

12. Does MPT make sense for income-focused investors?

Yes, MPT can be useful for income-focused investors. These investors might be more interested in assets that generate regular income, like bonds or dividend-paying stocks. MPT can guide these investors in building a diversified portfolio of income-generating assets that balances the trade-off between income, risk, and potential capital appreciation.

13. Does MPT assume all investors have the same information and expectations?

It’s true that MPT, in its pure form, assumes that all investors have access to the same information and make the same choices in a given situation. This is known as the assumption of “homogeneous expectations.” However, in real-world investing, this isn’t the case. Individual investors have different information, resources, and expectations. While the theory assumes homogeneous expectations, portfolio managers understand this limitation and adjust their strategies accordingly.

14. Can MPT not account for black swan events?

Like any model based on historical data, MPT struggles to account for rare, unforeseen events (often called “black swan” events). These events can cause dramatic market movements not captured by historical risk and correlation estimates. However, this is a challenge for any investment strategy, not just MPT. While MPT may not predict these events, its emphasis on diversification can help mitigate their impact.

15. How does MPT view Inflation-Protected Securities?

Inflation-protected securities, such as Treasury Inflation-Protected Securities (TIPS) in the US, can be included in an MPT-based portfolio. These securities offer a real return adjusted for inflation, providing a hedge against inflation risk. The expected returns, risks, and correlations of these securities with other assets will be considered in the MPT analysis.

Related information

Refer to the related knowledge resources:

QuietGrowth has been publishing content in this blog or in other sections of the website. Contributors for this content may include the employees of QuietGrowth, or third-party firms, or third-party authors. Unless otherwise noted, such content does not necessarily represent the actual views or opinions of QuietGrowth or any of its employees, directors, or officers.

Any links provided in our website to other websites are for the purpose of convenience, or as required by any such other websites. Unless otherwise noted, this does not imply that QuietGrowth endorses, is affiliated, and/or promotes any information, or products or services of those websites. Please read the advice disclaimer section of the website too.

Get started. Start investing.

Select the type of investment account you want to create




Individual: A personal account for you to invest for yourself.
Joint: An account for you and another person to invest for both of you.
SMSF: An account for the trustees of a Self-Managed Super Fund to invest through it.
Trust: An account for the trustees of a trust to invest through it.
Let QuietGrowth manage your investments for you.