Thursday, December 5, 2024

Monte Carlo simulations: forecast folly?

introduction

The Shanghai Stock Exchange Composite Index (SSE) boomed in early 2015, and because it soared, hordes of latest investors flocked to try their luck in securities speculation. Although stock bubbles were nothing latest, this one had two distinctive features. Firstly, under the regulatory framework, SSE shares weren’t allowed to rise or fall by greater than 10% on any day, resulting in some unusual looking share price charts after several months of a bull market. Second, many retail investors focused on buying “cheap” stocks or those trading below 20 renminbi (RMB).

Like all bubbles, this one eventually dissolved. The SSE plunged almost 40% between June and September 2015, teaching many novice investors the difference between price and valuation. A stock trading for $5 could be excessively expensive, just as a stock trading for $1,000 is usually a bargain.

While experienced investors understand this intuitively, many financial advisors still make similar mistakes. On any given day, they meet with potential and existing clients to debate their financial prospects. At the guts of those discussions are forecasts, often in the shape of Monte Carlo simulations, that estimate the worth of the client’s investment portfolio on the expected retirement date.

Here’s why it is a flawed approach and why there may be a greater approach to predict future returns.

Expected returns

Thousands of metrics have been tested across time periods and regions, but there isn’t a evidence that any investor, even equipped with them Strategies based on artificial intelligence (AI)., can predict individual stock prices or that of your entire market within the short to medium term. If it were different, mutual fund and hedge fund managers would do that Generate more alpha.

It needs to be easier to forecast long-term expected returns. Although not an ideal ratio, S&P 500 returns over the following decade are likely to reflect the present earnings yield, or the inverse of the price-to-earnings (P/E) ratio. In other words, valuations matter, and the upper the earnings yield today, the upper the expected returns 10 years from now.


US stock returns vs. initial earnings returns

Chart showing US stock returns compared to initial earnings returns

Sources: Online data Robert ShillerFinominal


US investment grade bonds over the past 20 years further illustrate the connection between expected long-term returns and current valuations. The bond’s initial yield was the annual return for the following 10 years. For example, if the present bond yield is 2%, the expected return for the following 10 years might be 2% per yr. So you get what you pay for.


US bond yields in comparison with initial bond yields

Chart showing US bond yields compared to initial bond yields

Source: Finominal


The folly of Monte Carlo simulations

Financial advisors rarely use stock and bond market valuations to make their long-term forecasts. Rather, they mostly run Monte Carlo simulations that do not take valuations under consideration in any respect. The inputs to those simulations are historical prices and a few model assumptions, while the output is a spread of expected returns with a given probability and assuming a traditional distribution. The range of expected returns for a portfolio could be 13.45%, with a lower quartile expectation of -0.63% and an upper quartile expectation of 25.71%, with a probability of 85%.

Such a result will only confuse most clients, but even when this just isn’t the case, the underlying method is flawed and shouldn’t be applied to investment portfolios. All financial products carry the identical warning: past performance just isn’t indicative of future results. Just since the stock market has been rising for years does not imply that may all the time be the case.

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We can pick a couple of cut-off dates—January 2000, November 2007, and December 2007, for instance—when the S&P 500 return was miles away from the actual 12-month return. Of course, the S&P 500’s P/E ratio reached record levels during these moments. But that just isn’t input for a Monte Carlo simulation.


Actual US stock returns in comparison with forecast Monte Carlo returns

Chart showing actual US stock returns versus forecast Monte Carlo returns

Source: Finominal


We can select similar time periods for U.S. investment grade bond markets, equivalent to December 2008, July 2012, or August 2020, when yields hit record lows. At these points, Monte Carlo simulations would remember attractive past returns and forecast the identical performance in the long run.

However, bonds turn out to be structurally unattractive above certain yields. European and Japanese bond returns have been negative over the past five years – but not if we only checked out Monte Carlo simulations based on past performance.


Actual 10-year US Treasury yields in comparison with forecast Monte Carlo yields

Chart showing actual 10-year U.S. Treasury yields versus forecast Monte Carlo yields

Source: Finominal


Capital market assumptions

For those forecasting expected returns for an investment portfolio, capital market assumptions are a substitute for Monte Carlo simulations. The process is way simpler and only requires the capital market assumptions available for various asset classes and equity aspects from different investment banks and asset managers, in addition to an element exposure evaluation of the portfolio. These could be differentiated into upside, base and downside cases in order that the forecast provides a practical range of outcomes. Tools to assist achieve this are freely available. Finominals Return predictorcan, for instance, estimate the return contributions for a diversified portfolio of stocks and bonds.


Contribution to the projected annual return of a diversified portfolio

Chart showing the contribution to the projected annual returns of a diversified portfolio

Source: Finominal


More thoughts

Monte Carlo simulations have obvious flaws, but so do capital market assumptions. Both market analysts and economists have a poor track record in terms of making accurate forecasts. If they were good at it, they might be fund managers who would generate income from their forecasts. As it stands, no fund manager can manage the market consistently.

However, asset managers rely heavily on valuations to create their capital market assumptions, which can make them preferable to simpler Monte Carlo simulations based on past performance. Regardless of the strategy, the predictions are certain to be incorrect, but one approach is barely dumber than the opposite.

Further insights from Nicolas Rabener and the Finominal Team, enroll for her Research reports.

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Photo credit: ©Getty Images / LemonTreeImages


Tags: dividends, investment management strategies, investing

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