经济学人下载:六大经济思想之五:纳什均衡(下)

As he struggled with ill health, however, his equilibrium became more and more central to the discipline.
然而，就在他与病痛搏斗时，他的均衡之于这门学科变得越来越核心了。

The share of economics papers citing the Nash equilibrium has risen sevenfold since 1980, and the concept has been used to solve a host of real-world policy problems.
自1980年以来，引用纳什均衡的经济学论文的比例上升了7倍。同时，这一概念还被用在了解决现实生活中的一系列政策问题上面。

One famous example was the American hospital system, which in the 1940s was in a bad Nash equilibrium.
一个著名的例子是美国医院体系。20世纪40年代，这一体系处于一种糟糕的纳什均衡之中。

Each individual hospital wanted to snag the brightest medical students.
每一家单独的医院都想争取到最好的医学学生。

With such students particularly scarce because of the war, hospitals were forced into a race whereby they sent out offers to promising candidates earlier and earlier.
由于这类学生因为战争而非常稀缺，各家医院之间被迫进入了一种越来越早地给有前途的候选人开出价码的竞争之中。

What was best for the individual hospital was terrible for the collective: hospitals had to hire before students had passed all of their exams.
个别医院的最佳是医院这一集体的噩梦：医院不得不在学生通过所有考试前雇佣他们。

Students hated it, too, as they had no chance to consider competing offers.
同时，由于没有机会考虑竞争开价，学生也痛恨这一体系。

Despite letters and resolutions from all manner of medical associations, as well as the students themselves, the problem was only properly solved after decades of tweaks, and ultimately a 1990s design by Elliott Peranson and Alvin Roth (who later won a Nobel economics prize of his own) .
尽管有来自学生自身以及各种医疗协会的信函和决议，这个问题在经历了数十年的微调后，并且最后是由埃利奥特·佩兰森和阿尔文·罗斯 (阿尔文·罗斯后来获得了自己的诺贝尔经济学奖) 在上世纪90年代的一个设计才得以恰当地解决。

Today, students submit their preferences and are assigned to hospitals based on an algorithm that ensures no student can change their stated preferences and be sent to a more desirable hospital that would also be happy to take them, and no hospital can go outside the system and nab a better employee.
如今，学生发出他们的意向，然后再根据一种在确保没有学生能够改变既定倾向的同时，还能够保证学生是被派往更渴望得到他们因而也会更乐意接收他们的医院，并且还能够保证没有医院能够跳出这一体系去争抢更好的雇员的算法被派往医院。

The system harnesses the Nash equilibrium to be self-reinforcing: everyone is doing the best they can based on what everyone else is doing.
这个体系利用纳什均衡实现了自我强化：每一个人都在根据其他每一个人正在做什么而尽可能地做事。

Other policy applications include the British government's auction of 3G mobile-telecoms operating licences in 2000.
其他的政策应用包括英国政府在2000年的3G移动通讯运营牌照的拍卖。

It called in game theorists to help design the auction using some of the insights of the Nash equilibrium, and ended up raising a cool ￡22.5 billion ($35.4 billion) —though some of the bidders' shareholders were less pleased with the outcome.
当时，它征召了多位博弈论专家，运用纳什均衡的一些洞见来帮助他们设计这次拍卖。最终，拍卖被加价到225亿英镑 (合354亿美元) ——尽管有些出价者的股东不太满意这个结果。

Nash's insights also help to explain why adding a road to a transport network can make journey times longer on average.
纳什的洞见还有助于解释为什么给交通网增加一条路会让旅行时间平均变得更长。

Self-interested drivers opting for the quickest route do not take into account their effect of lengthening others' journey times, and so can gum up a new shortcut.
选择最快路径的自私驾驶员没有考虑他们的行为对于延长其他人旅行时间的影响。因而，可能堵塞一条新的捷径。

A study published in 2008 found seven road links in London and 12 in New York where closure could boost traffic flows.
2008年发表的一篇论文在伦敦和纽约分别发现了7处和12处关闭了就可能提高交通流量的路口。

The Nash equilibrium would not have attained its current status without some refinements on the original idea.
纳什均衡要是没有对原始思想的某些改进是不会获得当前这种地位的。

First, in plenty of situations, there is more than one possible Nash equilibrium.
首先，在足够多的情形下，不止有一种可能的纳什均衡。

Drivers choose which side of the road to drive on as a best response to the behaviour of other drivers—with very different outcomes, depending on where they live;
作为对其他司机行为的最佳应对——结果大相径庭，司机选择走道路的哪一边取决于他们住在哪里；

they stick to the left-hand side of the road in Britain, but to the right in America.
在英国，他们坚持走道路的左侧；但是，在美国，他们坚持走右侧。

Much to the disappointment of algebra-toting economists, understanding strategy requires knowledge of social norms and habits.
让配备了代数的经济学家大失所望的是，理解策略需要社会规范和习俗的知识。

Nash's theorem alone was not enough.
单单是纳什的理论是不够的。

A second refinement involved accounting properly for non-credible threats.
第二次改进牵扯到了对于不可信威胁的正确估计。

If a teenager threatens to run away from home if his mother separates him from his mobile phone, then there is a Nash equilibrium where she gives him the phone to retain peace of mind.
如果男孩因为母亲把手机拿走就以离家出走相威胁的话，那么，在母亲把手机还给他以求得安心的行为中就存在一种纳什均衡。

But Reinhard Selten, a German economist who shared the 1994 Nobel prize with Nash and John Harsanyi, argued that this is not a plausible outcome.
但是，与纳什和约翰·海萨尼共同分享了1994年诺奖的德国经济学家赖因哈德·泽尔腾指出，这不是一种貌似合理的结果。

The mother should know that her child's threat is empty—no matter how tragic the loss of a phone would be, a night out on the streets would be worse.
母亲应当知道，孩子的威胁是空洞的——不管失去手机多么不幸，露宿街头只会更糟糕。

She should just confiscate the phone, forcing her son to focus on his homework.
她就是应当没收手机，强迫儿子用心做作业。

Mr Selten's work let economists whittle down the number of possible Nash equilibria.
泽尔腾的研究让经济学家减少了可能的纳什均衡的数量。

Harsanyi addressed the fact that in many real-life games, people are unsure of what their opponent wants.
海萨尼阐述了在众多现实生活的博弈中，人们不确定对手想要什么的事实。

Economists would struggle to analyse the best strategies for two lovebirds trying to pick a mutually acceptable location for a date with no idea of what the other prefers.
经济学家会设法去分析完全不知道对方的喜好而正在试图为一次约会选定一处相互都可接受地点的情侣的最佳策略。

By embedding each person's beliefs into the game (for example that they correctly think the other likes pizza just as much as sushi) , Harsanyi made the problem solvable.
利用将每一个人的期望植入博弈的方法 (例如，他们正确地认为对方像喜欢寿司一样喜欢披萨)，海萨尼让这一问题变得可以解决了。

A different problem continued to lurk.
一个不同的问题继续隐藏。

The predictive power of the Nash equilibrium relies on rational behaviour.
纳什均衡的预测力依赖于理性行为。

Yet humans often fall short of this ideal.
然而，人类经常达不到这种完美。

In experiments replicating the set-up of the prisoner's dilemma, only around half of people chose to confess.
在重复囚徒困境设置的实验中，只有一半的人选择坦白。

For the economists who had been busy embedding rationality (and Nash) into their models, this was problematic.
对于一直在忙着将理性 (和纳什) 植入他们模型中的经济学家来说，这很成问题。

What is the use of setting up good incentives, if people do not follow their own best interests?
如果人们不顺应自身的最佳利益，设置完美的激励有什么用呢？

All was not lost.
所有人都没有输。

The experiments also showed that experience made players wiser; by the tenth round only around 10% of players were refusing to confess.
这些实验还表明，经历让参与者更明智；到第十轮时，只有大约10%的参与者拒绝坦白。

That taught economists to be more cautious about applying Nash's equilibrium.
这教给经济学家要对应用纳什均衡更加谨慎。

With complicated games, or ones where they do not have a chance to learn from mistakes, his insights may not work as well.
至于复杂的或是他们没有机会从错误中吸取教训的博弈，他的洞见真可能不是很管用。

The Nash equilibrium nonetheless boasts a central role in modern microeconomics.
然而，纳什均衡仍在当代微观经济中享有一种核心地位。

Nash died in a car crash in 2015; by then his mental health had recovered, he had resumed teaching at Princeton and he had received that joint Nobel—in recognition that the interactions of the group contributed more than any individual.
2015年，纳什在一次车祸中身亡；那时，他的精神健康已经恢复并在普林斯顿重执教鞭，并且接受了那次联合诺奖——等于是承认：较之个人，集体互动功莫大焉。