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Do You Have to Be Good at Maths to Invest?

Being very good at maths is required for several investment fields. But none of these endeavours would seem to matter to the long-term investor

John Rekenthaler 6 February, 2017 | 10:00AM

Famously, Sir Isaac Newton lost nearly his entire net worth, £20,000 pounds, equivalent to about £3 million in today’s money, investing in one of the earliest stocks available. The South Sea Company was granted a monopoly by the British Crown in trade with Spanish South America in exchange for assuming the country’s war debt. Newton profited initially but kept buying on the way up, as the stock appreciated sharply, which cost him dearly when the shares collapsed to their original price.

Newton’s response, “I can calculate the motions of heavenly bodies, but not the madness of men,” tells half the story. Yes, investor irrationality does not lend itself to mathematics. Newton could not measure the temporary sanity of those who bought South Seas shares. But his maths challenge went deeper than that. He also had no tools with which to gauge South Sea’s business prospects. The calculus solves many problems, but not that of estimating how much trade will be generated with the colonies of an opposing superpower.

Thus, he could just as well have said, “I can calculate the motions of heavenly bodies, but not the profits of emerging ventures.” In other words, Newton would have been no better than the rest of us at understanding how Apple will fare under Tim Cook.

When Maths Matters

To be sure, being very good at maths is required for several investment fields. One is arbitrage; judging if a cheaper alternative can be substituted for an existing investment. Because the latter is a precisely known quantity, it is a matter of calculation to determine if the substitute is a better bargain. The computations can get complex indeed for derivatives, which is why Nobel Prizes were awarded to those who solved the code for options pricing and why the big banks hire bushels of quantitative Ph.D.s each year, but maths it is.

Another field is trading. This subject, admittedly, I know very little about, as the mutual funds and exchange-traded funds that comprise my field hire few such experts. But I have met those who work at firms that buy and sell securities, and the first thing those companies do when hiring is test their prospective traders on a series of mathematical puzzles. The maths is not of a high level, but getting correct answers requires an agile mind. Those who are not unusually adept with numeric patterns are rejected.

Finally, there is the growing field of data mining, or, as those practitioners would have it, evidence-based research. As each year passes, investment databases and computational powers grow larger, which permits deeper, more-complex searches through the historical records, seeking investment “factors” that appear to have been successful. This is the hunting ground of finance and economics Ph.D.s. The math required to sift through these reams of data is not novel, but it is a specialised skill. Ordinary mortals need not apply.

And Where It Doesn’t

But none of these endeavours would seem to matter to us, the long-term investor. We neither arbitrage nor day-trade, and while we might very well purchase the outputs of the evidence-based researchers, in the form of “strategic beta” ETFs, we don’t create those funds ourselves. Maths does little good in judging the claims of ETF providers.

The critical item is judgment, understanding when the reputed investment factors might be economically grounded and thus sustainable, as opposed to when they were accidental and do not figure to repeat. For us, too much maths can be a drawback. It can mislead.

Sir Isaac Newton’s South Seas debacle is typically told as a parable of the dangers of market manias, which can consume even the brightest of investors. That is true. However, Newton’s South Seas adventure also illustrates another, less commonly acknowledged point: Many critical investment questions cannot be solved by maths. And devoting too much attention to matters quantitative, while giving insufficient attention to issues such as judgment and data quality, can be outright harmful to portfolio results.

The information contained within is for educational and informational purposes ONLY. It is not intended nor should it be considered an invitation or inducement to buy or sell a security or securities noted within nor should it be viewed as a communication intended to persuade or incite you to buy or sell security or securities noted within. Any commentary provided is the opinion of the author and should not be considered a personalised recommendation. The information contained within should not be a person's sole basis for making an investment decision. Please contact your financial professional before making an investment decision.

About Author John Rekenthaler

John Rekenthaler  John Rekenthaler is vice president of research for Morningstar.