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This is not what I was taught in undergraduate economics — but experimental economics offers conclusive evidence of a core flaw in the efficient market hypothesis. Here’s a recent Atlantic summary of some of the research:

…Before financially sophisticated readers drag out their calculators, look up interest rates, and compute the present value of those future payments, I have a confession to make. You can’t buy this security, and it doesn’t really pay dividends every four weeks. It pays every four minutes, in a computer lab, to volunteers in economic experiments.

For more than two decades, economists have been running versions of the same experiment. They take a bunch of volunteers, usually undergraduates but sometimes businesspeople or graduate students; divide them into experimental groups of roughly a dozen; give each person money and shares to trade with; and pay dividends of 24 cents at the end of each of 15 rounds, each lasting a few minutes. (Sometimes the 24 cents is a flat amount; more often there’s an equal chance of getting 0, 8, 28, or 60 cents, which averages out to 24 cents.) All participants are given the same information, but they can’t talk to one another and they interact only through their trading screens. Then the researchers watch what happens, repeating the same experiment with different small groups to get a larger picture.

The great thing about a laboratory experiment is that you can control the environment. Wall Street securities carry uncertainties—more, lately, than many people expected—but this experimental security is a sure thing. “The fundamental value is unambiguously defined,” says the economist Charles Noussair, a professor at Tilburg University, in the Netherlands, who has run many of these experiments. “It’s the expected value of the future dividend stream at any given time”: 15 times 24 cents, or $3.60 at the end of the first round; 14 times 24 cents, or $3.36 at the end of the second; $3.12 at the end of the third; and so on down to zero. Participants don’t even have to do the math. They can see the total expected dividends on their computer screens.

Here, finally, is a security with security—no doubt about its true value, no hidden risks, no crazy ups and downs, no bubbles and panics. The trading price should stick close to the expected value.

At least that’s what economists would have thought before Vernon Smith, who won a 2002 Nobel Prize for developing experimental economics, first ran the test in the mid-1980s. But that’s not what happens. Again and again, in experiment after experiment, the trading price runs up way above fundamental value. Then, as the 15th round nears, it crashes. The problem doesn’t seem to be that participants are bored and fooling around. The difference between a good trading performance and a bad one is about $80 for a three-hour session, enough to motivate cash-strapped students to do their best. Besides, Noussair emphasizes, “you don’t just get random noise. You get bubbles and crashes.” Ninety percent of the time.

So much for security.

These lab results should give pause not only to people who believe in efficient markets, but also to those who think we can banish bubbles simply by curbing corruption and imposing more regulation. Asset markets, it seems, suffer from irrepressible effervescence. Bubbles happen, even in the most controlled conditions.

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But people do learn. By the third time the same group goes through a 15-round market, the bubble usually disappears. Everybody knows what the security is worth and realizes that everybody else knows the same thing. Or at least that’s what economists assumed was happening. But work that Noussair and his co-authors published in the December 2007 American Economic Review suggests that traders don’t reason that way.

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For those of us who invest our money outside the lab, this research carries two implications.

First, beware of markets with too much cash chasing too few good deals. When the Federal Reserve cuts interest rates, it effectively frees up more cash to buy financial instruments. When lenders lower down-payment requirements, they do the same for the housing market. All that cash encourages investment mistakes.

Second, big changes can turn even experienced traders into ignorant novices. Those changes could be the rise of new industries like the dot-coms of the 1990s or new derivative securities created by slicing up and repackaging mortgages. I asked the Caltech economist Charles Plott, one of the pioneers of experimental economics, whether the recent financial crisis might have come from this kind of inexperience. “I think that’s a good thesis,” he said. With so many new instruments, “it could be that the inexperienced heads are not people but the organizations themselves. The organizations haven’t learned how to deal with the risk or identify the risk or understand the risk.”

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