Monday, February 15, 2010

Reading "The Invincible Market Hypothesis"

Rajiv Sethi, the professor at Columbia University & Santa Fe Institute, had a post yesterday that is worth reading in full. Here are some highlights for the lazy soul:

This passage illustrates very clearly the limited value of informational efficiency when allocative efficiency fails to hold. Prices may indeed contain "all relevant information" but this includes not just beliefs about earnings and discount rates, but also beliefs about "sentiment and emotion." These latter beliefs can change capriciously, and are notoriously difficult to track and predict. Prices therefore send messages that can be terribly garbled, and resource allocation decisions based on these prices can give rise to enormous (and avoidable) waste. Provided that major departures of prices from intrinsic values can be reliably identified, a case could be made for government intervention in affecting either the prices themselves, or at least the responses to the signals that they are sending.

Under these conditions it makes little sense to say that markets are efficient, even if they are essentially unpredictable in the short run. Lorenzo at Thinking Out Aloud suggests a different name: other things in economics, such as rational expectations, EMH needs a better name. It is really something like the "all-information-is-incorporated hypothesis" just as rational expectations is really consistent expectations. If they had more descriptive names, people would not misconstrue them so easily and there would be less argument about them.

But a name that emphasizes informational efficiency is also misleading, because it does not adequately capture the range of non-fundamental information on market psychology that prices reflect. My own preference (following Jason Zweig) would be to simply call it the invincible markets hypothesis.

Well, for the lovers of complexity theory and computer science here comes the cake!

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