This is an excellent article put out in The New York Times
Annals of Economics
Rational Irrationality
The real reason that capitalism is so crash-prone.
by John Cassidy October 5, 2009
Rational Irrationality;
Wall Street;
Economic Crisis;
Millennium Bridge;
Hyun Song Shin;
Great Crunch;
Financial Markets
On June 10, 2000, Queen Elizabeth II opened the high-tech Millennium Bridge, which traverses the River Thames from the Tate Modern to St. Paul’s Cathedral. Thousands of people lined up to walk across the new structure, which consisted of a narrow aluminum footbridge surrounded by steel balustrades projecting out at obtuse angles. Within minutes of the official opening, the footway started to tilt and sway alarmingly, forcing some of the pedestrians to cling to the side rails. Some reported feeling seasick. The authorities shut the bridge, claiming that too many people were using it. The next day, the bridge reopened with strict limits on the number of pedestrians, but it began to shake again. Two days after it had opened, with the source of the wobble still a mystery, the bridge was closed for an indefinite period.
Some commentators suspected the bridge’s foundations, others an unusual air pattern. The real problem was that the designers of the bridge, who included the architect Sir Norman Foster and the engineering firm Ove Arup, had not taken into account how the footway would react to all the pedestrians walking on it. When a person walks, lifting and dropping each foot in turn, he or she produces a slight sideways force. If hundreds of people are walking in a confined space, and some happen to walk in step, they can generate enough lateral momentum to move a footbridge—just a little. Once the footway starts swaying, however subtly, more and more pedestrians adjust their gait to get comfortable, stepping to and fro in synch. As a positive-feedback loop develops between the bridge’s swing and the pedestrians’ stride, the sideways forces can increase dramatically and the bridge can lurch violently. The investigating engineers termed this process “synchronous lateral excitation,” and came up with a mathematical formula to describe it.
What does all this have to do with financial markets? Quite a lot, as the Princeton economist Hyun Song Shin pointed out in a prescient 2005 paper. Most of the time, financial markets are pretty calm, trading is orderly, and participants can buy and sell in large quantities. Whenever a crisis hits, however, the biggest players—banks, investment banks, hedge funds—rush to reduce their exposure, buyers disappear, and liquidity dries up. Where previously there were diverse views, now there is unanimity: everybody’s moving in lockstep. “The pedestrians on the bridge are like banks adjusting their stance and the movements of the bridge itself are like price changes,” Shin wrote. And the process is self-reinforcing: once liquidity falls below a certain threshold, “all the elements that formed a virtuous circle to promote stability now will conspire to undermine it.” The financial markets can become highly unstable.
This is essentially what happened in the lead-up to the Great Crunch. The trigger was, of course, the market for subprime-mortgage bonds—bonds backed by the monthly payments from pools of loans that had been made to poor and middle-income home buyers. In August, 2007, with house prices falling and mortgage delinquencies rising, the market for subprime securities froze. By itself, this shouldn’t have caused too many problems: the entire stock of outstanding subprime mortgages was about a trillion dollars, a figure dwarfed by nearly twelve trillion dollars in total outstanding mortgages, not to mention the eighteen-trillion-dollar value of the stock market. But then banks, which couldn’t estimate how much exposure other firms had to losses, started to pull back credit lines and hoard their capital—and they did so en masse, confirming Shin’s point about the market imposing uniformity. An immediate collapse was averted when the European Central Bank and the Fed announced that they would pump more money into the financial system. Still, the global economic crisis didn’t ease up until early this year, and by then governments had committed an estimated nine trillion dollars to propping up the system.
* from the issue
* cartoon bank
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A number of explanations have been proposed for the great boom and bust, most of which focus on greed, overconfidence, and downright stupidity on the part of mortgage lenders, investment bankers, and Wall Street C.E.O.s. According to a common narrative, we have lived through a textbook instance of the madness of crowds. If this were all there was to it, we could rest more comfortably: greed can be controlled, with some difficulty, admittedly; overconfidence gets punctured; even stupid people can be educated. Unfortunately, the real causes of the crisis are much scarier and less amenable to reform: they have to do with the inner logic of an economy like ours. The root problem is what might be termed “rational irrationality”—behavior that, on the individual level, is perfectly reasonable but that, when aggregated in the marketplace, produces calamity.
Consider the freeze that started in August of 2007. Each bank was adopting a prudent course by turning away questionable borrowers and holding on to its capital. But the results were mutually ruinous: once credit stopped flowing, many financial firms—the banks included—were forced to sell off assets in order to raise cash. This round of selling caused stocks, bonds, and other assets to decline in value, which generated a new round of losses.
A similar feedback loop was at work during the boom stage of the cycle, when many mortgage companies extended home loans to low- and middle-income applicants who couldn’t afford to repay them. In hindsight, that looks like reckless lending. It didn’t at the time. In most cases, lenders had no intention of holding on to the mortgages they issued. After taking a generous fee for originating the loans, they planned to sell them to Wall Street banks, such as Merrill Lynch and Goldman Sachs, which were in the business of pooling mortgages and using the monthly payments they generated to issue mortgage bonds. When a borrower whose home loan has been “securitized” in this way defaults on his payments, it is the buyer of the mortgage bond who suffers a loss, not the issuer of the mortgage.
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