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Tuesday, December 25, 2012

EMH vs Macro, Fischer Black

Arnold Kling on the tension between macroeconomics and the Efficient Markets Hypothesis (EMH). I'm surprised this isn't more often noticed by economists. But I suppose macro types don't tend to think deeply about finance (at least, not before the recent crisis; how many macro types actually understand Black-Scholes-Merton?) and vice versa. I was shocked at the beginning of the credit crisis to meet famous macroeconomists who didn't know what a credit default swap was, and I still often meet finance types who laugh at macro models.
askblog: Consider financial variables, such as the long-term interest rate or the price-earnings ratio of the overall stock market. According to the efficient markets hypothesis, these are not predictable on the basis of known information. To put this another way, you cannot beat the market forecast for these variables.

On the other hand, in conventional macroeconomics these variables can be predicted using models and controlled using policy levers. Reconciling this with the EMH has challenged economists for decades. ...

I prefer a third way of looking at things, which might be expressed in the work by Frydman and Goldberg. That is, there is no reason for all participants in markets to be using the same model. They have different information sets. The EMH is a useful guide to everyone, because it serves as a reminder that it is unwise to assume that your information set is somehow superior. However, it is not correct to impose “rational expectations,” in which everyone uses the same model.

... Incidentally, I recently re-read Perry Mehrling’s biography of Fischer Black. Black was perhaps the first economist to think about the contrast between modern finance theory and conventional macro, and Black was the first and perhaps the only one to attempt to recast macro entirely in terms of modern finance.
More thoughts on EMH here. My comments on Mehrling's bio and Fischer Black are here.
... on the topic of finance books, I highly recommend this biography of Fischer Black, which I should have reviewed here long ago. Fischer was yet another outsider (his background was in theoretical physics) to finance who made an important contribution. Unlike Kelly, he was accorded mainstream recognition (professorship at Chicago and partnership at Goldman) during his career. The most impressive thing about Black was his ability to think deeply and independently -- beyond the conventional wisdom. There are some very intriguing passages in the book about his views on money and banking which are, I think, quite unconventional to mainstream economics.

... Black was both an undergrad and grad student at Harvard in physics. He didn't really complete his PhD in physics, but sort of drifted into AI-related stuff(!) at MIT, under cover of math or applied math.

The bio says the only course he ever had trouble with was Schwinger's course on advanced quantum. The biographer suggests Black did poorly due to lack of interest, but I find that hard to believe given the subject matter, the lecturer and the times ;-)

Black's point of view was clearly that of a physicist or applied mathematician. He really was a fascinating guy, and the biographer, being an academic economist, can appreciate a lot of Black's thinking -- it's not an entirely superficial book despite being non-technical.

After reading the book, I don't feel so bad about questioning some of the fundamental assumptions made by academic economists. Black was asking some of the very same questions during his career.

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