今回ノーベル賞を受賞したロバート・シラーがNYTへの寄稿をそう題している。原題は「Sharing Nobel Honors, and Agreeing to Disagree」。

The Nobel Memorial Prize in Economic Science has sometimes been awarded to economists who disagree profoundly. Notably, in 1974, the Nobel committee gave a joint prize to Gunnar Myrdal, a Social Democrat in Sweden and a proponent of the welfare state, and Friedrich Hayek, a conservative who believed that government should be minimal.

This time, the prize given to Eugene Fama and Lars Peter Hansen of the University of Chicago and me for “empirical analysis of asset prices” is similarly discordant. So many people have been asking me about this obvious incongruity that I thought I should address it directly here.
Professor Fama is the father of the modern efficient-markets theory, which says financial prices efficiently incorporate all available information and are in that sense perfect. In contrast, I have argued that the theory makes little sense, except in fairly trivial ways. Of course, prices reflect available information. But they are far from perfect. Along with like-minded colleagues and former students, I emphasize the enormous role played in markets by human error, as documented in a now-established literature called behavioral finance.



Actually, I do not completely oppose the efficient-markets theory. I have been calling it a half-truth. If the theory said nothing more than that it is unlikely that the average amateur investor can get rich quickly by trading in the markets based on publicly available information, the theory would be spot on. I personally believe this, and in my own investing I have avoided trading too much, and have a high level of skepticism about investing tips.

But the theory is commonly thought, at least by enthusiasts, to imply much more. Notably, it has been argued that regular movements in the markets reflect a wisdom that transcends the best understanding of even the top professionals, and that it is hopeless for an ordinary mortal, even with a lifetime of work and preparation, to question pricing. Market prices are esteemed as if they were oracles.

This view grew to dominate much professional thinking in economics, and its implications are dangerous. It is a substantial reason for the economic crisis we have been stuck in for the past five years, for it led authorities in the United States and elsewhere to be complacent about asset mispricing, about growing leverage in financial markets and about the instability of the global system. In fact, markets are not perfect, and really need regulation, much more than Professor Fama's theories would allow.


Professor Fama avoids theories that describe these risk premia as even possibly reflecting irrational behavior, and I think he's wrong about that. Still, he has ended up with an investing approach that looks, in some of its fundamental principles at least, a little like my own.
I can even recommend that people might consider investing in DFA.

I would not, however, recommend that monetary or fiscal authorities seek inspiration from his theories on how to stabilize the economy. He doubts the existence of any bubble before this crisis, and his philosophy would have let banks fail at the beginning of it.


We disagree on a number of important points, but there is nothing wrong with our sharing the prize. In fact, I am happy to share it with my co-recipients, even if we sometimes seem to come from different planets.