Passage 6 Markets Are Like People
市场经济理论：从EMH到AMH 《新闻周刊》

[00:00]Remember when everybody thought that markets were all-knowing?
[00:05]Before the financial crisis struck in late 2008,
[00:10]the reigning dogma in economics was the "efficient-markets hypothesis,"
[00:16]an idea popularized by Eugene Fama that enjoyed exalted status
[00:21]for more than three decades. EMH, as economists call it,
[00:27]States that markets reflect all available information,
[00:31]that investors are rational, and that prices are stable.
[00:36]While anyone without a Ph.D.
[00:39]or an M.B.A. probably immediately recognized the flaws in such rigid thinking,
[00:45]these notions once seemed self-evident to academics and investors.
[00:51]The economists still vigorously defending them today sound like alcoholics
[00:57]denying they have a problem.
[01:00]Only when those programs led to financial products
[01:03]that helped blow up the world did the flaws in the theory become clear to all.
[01:10]A few people saw the trouble coming. All the way back in 2001,
[01:18]Joseph Stiglitz shared the Nobel Prize with two others for
[01:23]poking holes in the theory. Behavioral economists, too,
[01:29]have shown time and again that humans can act irrationally
[01:34]by falling prey to the herd mentality, for example.
[01:38]But those findings have been somewhat scattershot,
[01:42]with no principles to show how to apply them in the real world.
[01:47]Hence the quest for a new, grand theory,
[01:52]one that patches the holes in the efficient markets idea
[01:56]and integrates the wisdom of the behavioralists.
[02:01]Andrew Lo, an economist at MIT, thinks he has just the solution.
[02:08]Lo is the foremost proponent of something
[02:11]called the adaptive markets hypothesis,
[02:14]a way of looking at the markets through the prism of evolutionary biology.
[02:21]Rather than assuming markets always know best,
[02:25]AMH builds on an understanding that they sometimes don't.
[02:30]The trick is knowing when irrational behavior will lead to a bubble
[02:35]or even a global crisis. Lo believes the secret lies in
[02:40]studying the "ecology" of the markets.
[02:44]Just as biologists catalog species and map their fortunes over time,
[02:51]regulators and policymakers should categorize the market's many players.
[02:58]That means identifying the various hedge funds, pension funds,
[03:04]and other participants in any given market,
[03:08]and learning what kind of strategies are popular at a particular moment in time.
[03:14]"What is their biomass? How are they going to interact with each other?" Lo asks.
[03:22]Incredible as it seems, regulators don't collect this kind of information,
[03:29]because, according to EMH, everyone responds to incentives in the same basic way.
[03:37]But the adaptive-markets hypothesis holds
[03:40]that investors' behavior can vary depending on
[03:44]their psychology at any given moment.
[03:48]If their actions were tracked over time in a wide variety of settings,
[03:54]says Lo, "we could develop an extraordinarily good sense of
[03:59]how the markets behave." So far, however,
[04:05]it's been tough to get financial authorities to do this
[04:09]because high-level investors strongly resist divulging information
[04:14]about their strategies.