A4_Efficiency and beyond.pdfVIP

1 Efficiency and beyond The efficient-markets hypothesis has underpinned many of the financial industry’s models for years. After the crash, what remains of it? Jul 16th 2009 | NEW YORK | from PRINT EDITION The Economist Illustration by Brett Ryder IN 1978 Michael Jensen, an American economist, boldly declared that “there is no other proposition in economics which has more solid empirical evidence supporting it than the efficient-markets hypothesis” (EMH). That was quite a claim. The theory’s origins went back to the beginning of the century, but it had come to prominence only a decade or so before. Eugene Fama, of the University of Chicago, defined its essence: that the price of a financial asset reflects all available information that is relevant to its value. From that idea powerful conclusions were drawn, not least on Wall Street. If the EMH held, then markets would price financial assets broadly correctly. Deviations from equilibrium values could not last for long. If the price of a share, say, was too low, well-informed investors would buy it and make a killing. If it looked too dear, they could sell or short it and make money that way. It also followed that bubbles could not form—or, at any rate, could not last: some wise investor would spot them and pop them. And trying to beat the market was a fool’s errand for almost everyone. If the information was out there, it was already in the price. On such ideas, and on the complex mathematics that described them, was founded the Wall Street profession of financial engineering. The engineers designed derivatives and securitisations, from simple interest-rate options to ever more intricate credit-default swaps and collateralised debt obligations. All the while, confident in the theoretical underpinnings of their inventions, they reassured any doubters that all this activity was not just making bankers rich. It was making the financial system safer and the economy healthier. That is wh