Dr. P.V. Viswanath



Economics/Finance on the Web
Student Interest


Efficient Market Theory and the Crisis
By JEREMY J. SIEGEL, October 27, 2009, NY Times


Neither the rating agencies' mistakes nor the overleveraging by financial firms was the fault of an academic hypothesis.

Financial journalist and best-selling author Roger Lowenstein didn't mince words in a piece for the Washington Post this summer: "The upside of the current Great Recession is that it could drive a stake through the heart of the academic nostrum known as the efficient-market hypothesis." In a similar vein, the highly respected money manager and financial analyst Jeremy Grantham wrote in his quarterly letter last January: "The incredibly inaccurate efficient market theory [caused] a lethally dangerous combination of asset bubbles, lax controls, pernicious incentives and wickedly complicated instruments [that] led to our current plight."

But is the Efficient Market Hypothesis (EMH) really responsible for the current crisis? The answer is no. The EMH, originally put forth by Eugene Fama of the University of Chicago in the 1960s, states that the prices of securities reflect all known information that impacts their value. The hypothesis does not claim that the market price is always right. On the contrary, it implies that the prices in the market are mostly wrong, but at any given moment it is not at all easy to say whether they are too high or too low. The fact that the best and brightest on Wall Street made so many mistakes shows how hard it is to beat the market.

This does not mean the EMH can be used as an excuse by the CEOs of the failed financial firms or by the regulators who did not see the risks that subprime mortgage-backed securities posed to the financial stability of the economy. Regulators wrongly believed that financial firms were offsetting their credit risks, while the banks and credit rating agencies were fooled by faulty models that underestimated the risk in real estate.

After the 1982 recession, the U.S. and world economies entered into a long period where the fluctuations in variables such as gross domestic product, industrial production, and employment were significantly lower than they had been since World War II. Economists called this period the "Great Moderation" and attributed the increased stability to better monetary policy, a larger service sector and better inventory control, among other factors.

The economic response to the Great Moderation was predictable: risk premiums shrank and individuals and firms took on more leverage. Housing prices were boosted by historically low nominal and real interest rates and the development of the securitized subprime lending market.

According to data collected by Prof. Robert Shiller of Yale University, in the 61 years from 1945 through 2006 the maximum cumulative decline in the average price of homes was 2.84% in 1991. If this low volatility of home prices persisted into the future, a mortgage security composed of a nationally diversified portfolio of loans comprising the first 80% of a home's value would have never come close to defaulting. The credit quality of home buyers was secondary because it was thought that underlying collateral—the home—could always cover the principal in the event the homeowner defaulted. These models led credit agencies to rate these subprime mortgages as "investment grade."

But this assessment was faulty. From 2000 through 2006, national home prices rose by 88.7%, far more than the 17.5% gain in the consumer price index or the paltry 1% rise in median household income. Never before have home prices jumped that far ahead of prices and incomes.

This should have sent up red flags and cast doubts on using models that looked only at historical declines to judge future risk. But these flags were ignored as Wall Street was reaping large profits bundling and selling the securities while Congress was happy that more Americans could enjoy the "American Dream" of home ownership. Indeed, through government-sponsored enterprises such as Fannie Mae and Freddie Mac, Washington helped fuel the subprime boom.

Neither the rating agencies' mistakes nor the overleveraging by the financial firms in the subprime securities is the fault of the Efficient Market Hypothesis. The fact that the yields on these mortgages were high despite their investment-grade rating indicated that the market was rightly suspicious of the quality of the securities, and this should have served as a warning to prospective buyers.

With few exceptions (Goldman Sachs being one), financial firms ignored these warnings. CEOs failed to exercise their authority to monitor overall risk of the firm and instead put their faith in technicians whose narrow models could not capture the big picture. One can only wonder if the large investment banks would have taken on such risks when they were all partnerships and the lead partner had all his wealth in the firm, as they were just a few decades ago.

The misreading of these economic trends did not just reside within the private sector. Former Fed Chairman Alan Greenspan stated before congressional committees last December that he was "shocked" that the top executives of the financial firms exposed their stockholders to such risk. But had he looked at their balance sheets, he would have realized that not only did they put their own shareholders at risk, but their leveraged positions threatened the viability of the entire financial system.

As home prices continued to climb and subprime mortgages proliferated, Mr. Greenspan and current Fed Chairman Ben Bernanke were perhaps the only ones influential enough to sound an alarm and soften the oncoming crisis. But they did not. For all the deserved kudos that the central bank received for their management of the crisis after the Lehman bankruptcy, the failure to see these problems building will stand as a permanent blot on the Fed's record.

Our crisis wasn't due to blind faith in the Efficient Market Hypothesis. The fact that risk premiums were low does not mean they were nonexistent and that market prices were right. Despite the recent recession, the Great Moderation is real and our economy is inherently more stable.

But this does not mean that risks have disappeared. To use an analogy, the fact that automobiles today are safer than they were years ago does not mean that you can drive at 120 mph. A small bump on the road, perhaps insignificant at lower speeds, will easily flip the best-engineered car. Our financial firms drove too fast, our central bank failed to stop them, and the housing deflation crashed the banks and the economy.

Mr. Siegel, a professor of finance at the University of Pennsylvania's Wharton School, is the author of "Stocks for the Long Run," now in its 4th edition from McGraw-Hill.



  1. Does the EMH imply that prices are accurate?
  2. "(B)anks and credit rating agencies were fooled by faulty models that underestimated the risk in real estate." Doesn't this imply that banks and credit rating agencies did not use the information available to them? Doesn't that imply inefficient markets?
  3. "Never before have home prices jumped that far ahead of prices and incomes. This should have sent up red flags and cast doubts on using models that looked only at historical declines to judge future risk." So this means that somebody who looked at those red flags (and this information was available to everybody) could have made money by shortselling stocks. Is it's possible to earn an abnormal return, the market cannot be efficient. Right? Or wrong?