The Many Signs of Madness in Markets

Market madness has never been hard to diagnose. It’s almost two centuries since Charles Mackay published Extraordinary Popular Delusions and the Madness of Crowds. Benjamin Graham pioneered value investing in the 1930s by inviting everyone to think of “Mr. Market” as a manic-depressive who makes mistakes that can be exploited. And the Israeli psychologists Daniel Kahneman and Amos Tversky documented in seminal work in the 1960s and ’70s the behavioral biases or mental shortcuts — known as heuristics — that are hot-wired into the human mind and distort markets. For example, we are all driven by loss aversion and will take greater risks to avoid a loss than to make a profit of the same size.

Market prices are set by humans, who are fallible, so none of this should be surprising. There’s also voluminous research to show that in the very long term, our human foibles tend to cancel out and stock markets do expand in line with corporate profits and the growth in the economy. The language to describe these issues has been around for a long time. In a line generally attributed to Graham, as often cited by his disciple Warren Buffett, “In the short term the market is a voting machine; in the long term it’s a weighing machine.” Money can be made by exploiting others’ mistakes, but over time you should just strap in and follow the companies that perform the best.

See more: Market Valuation: Expensive CAPE Or Cheap PEG?

And John Maynard Keynes (allegedly) provided an aphorism, also as long ago as the 1930s, to explain why profiting from others’ irrationality, while tempting, is dangerous: “Markets can stay irrational longer than you can stay solvent.”

All of this literature has co-existed with the growth of a massive industry devoted to ignoring it. The efficient markets hypothesis, which holds that share prices will at all times incorporate all known information, and move in a “random walk”from news story to news story, is written into the assumptions that guide most investment models. There’s acceptance that human imperfection guarantees that this walk will not be truly random, but an edifice of algorithms, arbitrage models and indexes now exists to identify those errors, profit from them, and in the process help ensure that the market returns to its true path as a weigher of fundamentals, not a voting exercise.

So it doesn’t at first seem that there’s any great need for a new book called The Madness of Markets. But it turns out that Alex Edmans, the London Business School professor who has just published a book with that title, has indeed found fertile territory. Over the last few decades, ever increasing computer firepower has allowed academics to find and categorize ever more anomalies; Edmans’ book is a dazzling summation of all that evidence. It adds up to a stunning indictment of human weaknesses, with numbers attached. And he’s presented it as a how-to manual for investors to try to make money from others’ mistakes (even if Keynes’ warning will always be relevant).