经济学人下载:信息不对称之柠檬市场理论与效应(上)

Economics brief: six big ideas.
经济概要：六大经济思想。

Information asymmetry: Secrets and agents
信息不对称：秘密和代理

George Akerlof's 1970 paper, “The Market for Lemons”, is a foundation stone of information economics, the first in our series on seminal economic ideas.
六大经济思想之一，乔治·阿克洛夫1970年的论文——《柠檬市场》，它是信息经济学的一块基石。

In 2007 the state of Washington introduced a new rule aimed at making the labour market fairer: firms were banned from checking job applicants' credit scores.
2007年，华盛顿州引入了一项旨在让劳动力市场更公平的新法律：企业被禁止核查求职者的信用得分。

Campaigners celebrated the new law as a step towards equality—an applicant with a low credit score is much more likely to be poor, black or young.
发起这项运动的人欢呼庆祝，认为这是通向平等的一步——信用得分低的求职者极有可能是穷人、黑人或者年轻人。

Since then, ten other states have followed suit.
自那以后，又有十个州如法炮制。

But when Robert Clifford and Daniel Shoag, two economists, recently studied the bans, they found that the laws left blacks and the young with fewer jobs, not more.
但是，日前，当两位经济学家——罗伯特·克利福德和丹尼尔·绍格——研究了这些禁令时，他们发现，这些法律带给黑人和年轻人的工作更少了，而不是更多。

Before 1970, economists would not have found much in their discipline to help them mull this puzzle.
放在1970年之前，经济学家是不会在这门学科中找到太多的东西来帮助他们仔细思考这个迷的。

Indeed, they did not think very hard about the role of information at all.
实际上，他们当时根本就没有很努力地去思考信息的作用。

In the labour market, for example, the textbooks mostly assumed that employers know the productivity of their workers—or potential workers—and, thanks to competition, pay them for exactly the value of what they produce.
例如，那时的教科书大都假设，在劳动力市场中，雇主知道他们的工人——或者潜在的工人——的生产率，而且，由于竞争，是按照工人所生产的东西的价值给他们开工资的。

You might think that research upending that conclusion would immediately be celebrated as an important breakthrough.
人们可能认为，颠覆这一论断的研究立即会被誉为一项重大突破。

Yet when, in the late 1960s, George Akerlof wrote “The Market for Lemons”, which did just that, and later won its author a Nobel prize, the paper was rejected by three leading journals.
然而，当乔治·阿克洛夫于上世纪60年代末期写出恰恰实现了这种突破并为作者赢得了诺贝尔奖的《柠檬市场》时，这篇论文曾遭到三家主要期刊拒绝。

At the time, Mr Akerlof was an assistant professor at the University of California, Berkeley; he had only completed his PhD, at MIT, in 1966.
那时，阿克洛夫是加州大学伯克利分校的一名助教；仅于1966年在麻省理工完成了博士学位。

Perhaps as a result, the American Economic Review thought his paper's insights trivial.
也许是因为这个原因，《美国经济评论》认为他的论文的观点微不足道。

The Review of Economic Studies agreed.
《经济研究评论》同意了这个看法。

The Journal of Political Economy had almost the opposite concern: it could not stomach the paper's implications.
《 政治经济学杂志》有着几乎完全相反的担忧：它可能消化不了这篇论文深远意义。

Mr Akerlof, now an emeritus professor at Berkeley and married to Janet Yellen, the chairman of the Federal Reserve, recalls the editor's complaint: “If this is correct, economics would be different.”
如今已是伯克利分校名誉教授并同美联储主席珍妮特·耶伦成婚的阿克洛夫还记着那位编辑的不满：“如果这是正确的，经济学会截然不同。”

In a way, the editors were all right.
从某种程度上来说，这些编辑当时都是对的。

Mr Akerlof's idea, eventually published in the Quarterly Journal of Economics in 1970, was at once simple and revolutionary.
最终于1970年在《经济学季刊》上发表了的阿克洛夫的思想即是简单的，也是革命性的。

Suppose buyers in the used-car market value good cars— “peaches” —at $1,000, and sellers at slightly less.
假设，二手车市场中的买方给好车—— “桃子” ——估价1000美元，卖方要稍微少一点。

A malfunctioning used car—a “lemon” —is worth only $500 to buyers (and, again, slightly less to sellers) .
一辆瑕疵二手车—— “柠檬”，对买方而言，只值500美元 (而且对卖方来说，又要稍微少一点)。

If buyers can tell lemons and peaches apart, trade in both will flourish.
如果买方能够区分柠檬和桃子，两者的交易都会红火起来。

In reality, buyers might struggle to tell the difference: scratches can be touched up, engine problems left undisclosed, even odometers tampered with.
在现实中，买方可能会设法找出不同：刮痕可能被补上了，发动机问题可能未得到披露，甚至里程表都可能被篡改了。

To account for the risk that a car is a lemon, buyers cut their offers.
为了对车是柠檬的风险负责，买方大肆杀价。

They might be willing to pay, say, $750 for a car they perceive as having an even chance of being a lemon or a peach.
比如说，他们可能愿意为一辆他们认为有着或是柠檬或是桃子的同等几率的车支付750美元。

But dealers who know for sure they have a peach will reject such an offer.
但是，确切地知道自己的车是桃子的交易者将拒绝这样的出价。

As a result, the buyers face “adverse selection” : the only sellers who will be prepared to accept $750 will be those who know they are offloading a lemon.
结果，买方面临 “逆向选择” : 唯一准备接受750美元的卖家将是知道自己正在脱手柠檬的人。

Smart buyers can foresee this problem.
聪明的买方能预见到这个问题。

Knowing they will only ever be sold a lemon, they offer only $500.
由于知道自己永远只会被卖给柠檬，他们仅出价500美元。

Sellers of lemons end up with the same price as they would have done were there no ambiguity.
最后，柠檬的卖方得到的是与没有歧义时会得到的价格同样的价格。

But peaches stay in the garage.
但是，桃子还在仓库中。

This is a tragedy: there are buyers who would happily pay the asking-price for a peach, if only they could be sure of the car's quality.
这是一种悲剧：只要能确信汽车的质量，会高高兴兴地为桃子支付询价的买方是存在的。

This “information asymmetry” between buyers and sellers kills the market.
买卖双方之间的这种 “信息不对称” 杀死了市场。

Is it really true that you can win a Nobel prize just for observing that some people in markets know more than others?
仅仅因为观察到市场中的某些人比别人知道得多就能获得诺贝尔奖这种事是千真万确的吗？

That was the question one journalist asked of Michael Spence, who, along with Mr Akerlof and Joseph Stiglitz, was a joint recipient of the 2001 Nobel award for their work on information asymmetry.
这曾是一名记者向迈克尔·斯彭斯——这位与阿克洛夫和约瑟夫·斯蒂格利茨一起因为他们对信息不对称的研究而获得2001年诺贝尔奖的联合得主——问到的问题。

His incredulity was understandable.
他的怀疑是可以理解的。

The lemons paper was not even an accurate description of the used-car market: clearly not every used car sold is a dud.
柠檬论文甚至不是一篇关于二手车市场的精准描述：很明显，不是每一辆在售二手车都是有瑕疵的车。

And insurers had long recognised that their customers might be the best judges of what risks they faced, and that those keenest to buy insurance were probably the riskiest bets.
另外，保险商早就承认，他们的客户可能是其自身所面临的风险的最佳判定者，最急于要投保的可能是风险最大的赌博。

Yet the idea was new to mainstream economists, who quickly realised that it made many of their models redundant.
然而，这个思想对于主流经济学家来说全新的，他们很快就认识到它已让他们的许多模型显得多余。

Further breakthroughs soon followed, as researchers examined how the asymmetry problem could be solved.
没过多久，随着研究者检验不对称问题能得到怎样的解决，进一步的突破随之而来。

Mr Spence's flagship contribution was a 1973 paper called “Job Market Signalling” that looked at the labour market.
斯彭斯的主要贡献是1973年的一篇名为 “就业市场信号行为” 的考察劳动力市场的论文。

Employers may struggle to tell which job candidates are best.
雇主可能难以挑出最好的那个求职者。

Mr Spence showed that top workers might signal their talents to firms by collecting gongs, like college degrees.
斯彭斯指出，顶层的工人或许会以收集荣誉——如大学学位——的行为为信号，向企业展示自己的才华。

Crucially, this only works if the signal is credible: if low-productivity workers found it easy to get a degree, then they could masquerade as clever types.
关键是，这只有在信号是可信的时候才管用：如果低生产力的工人发现得到学位很容易，他们就可能把自己装扮成聪明之人。

This idea turns conventional wisdom on its head.
这一思想彻底颠覆了传统的智慧。

Education is usually thought to benefit society by making workers more productive.
一般认为，教育之有益于社会，是因为它让工人变得更高效。

If it is merely a signal of talent, the returns to investment in education flow to the students, who earn a higher wage at the expense of the less able, and perhaps to universities, but not to society at large.
如果它仅仅是才华的一个象征，教育投资的所得就会流向学生，使他们以才华较少之人为代价获得更高的工资；或者也可能是各个大学，但不是整个社会。

One disciple of the idea, Bryan Caplan of George Mason University, is currently penning a book entitled “The Case Against Education”.
这个思想的一位信徒——乔治梅森大学的布莱恩·卡普兰目前正在撰写一本名为《反对教育之种种》的书。

(Mr Spence himself regrets that others took his theory as a literal description of the world. )
(斯彭斯本人后悔的是，被人把他的理论当成是对这个世界的一种文字描述。)

Signalling helps explain what happened when Washington and those other states stopped firms from obtaining job-applicants' credit scores.
信号行为有助于解释华盛顿等州在阻止企业获得求职者信用得分时所发生了的事情。

Credit history is a credible signal: it is hard to fake, and, presumably, those with good credit scores are more likely to make good employees than those who default on their debts.
信用历史是一个可信的信号：它难以造假，而且，可以假定，信用得分良好的人比债务违约的人更有可能成为好雇员。

Messrs Clifford and Shoag found that when firms could no longer access credit scores, they put more weight on other signals, like education and experience.
克利福德先生和绍格先生发现，当企业不再能得到信用得分时，会把重点放在其他信号上面，如教育和资历。

Because these are rarer among disadvantaged groups, it became harder, not easier, for them to convince employers of their worth.
因为这些信号在弱势劣群体中较为少见，因而，对他们而言，让雇主相信自己的价值就变得更难，而不是更容易。