[2009.01.03] International bright young things 闪亮国际的经济学后生

Emerging economists
新兴经济学家

International bright young things
闪亮国际的经济学后生

Dec 30th 2008
From The Economist print edition

The next generation of economists do their best work somewhere between the field clinic and the dissection room
新一代的经济学家在实地考察与学院研究之间成就了他们的最佳工作

Illustration by Otto Dettmer

TWENTY years ago The Economist wrote about eight young economists who were making a big splash in their discipline and beyond. One of them, Paul Krugman, recently won the Nobel prize for his models of international trade and economic geography. Ten years later we tried to repeat the trick, identifying another eight young stars, many of whom were taking their discipline far off-piste. One has since achieved even greater fame than anticipated. Steven Levitt of the University of Chicago became a household name as co-author of “Freakonomics”, a bestselling book published in 2005.

20年前，本报对8位当时正在其领域内外引起轰动的年轻经济学家做了一次报道。身为其中之一，保罗·克鲁格曼(Paul Krugman)因其在国际贸易与经济地理学领域的贡献，而于最近获得了诺贝尔经济学奖。10年之后，我们故技重施，选定了另外8位新星。彼时，他们中的许多人都将自己的研究科目带进了新的未知领域。到如今，他们当中的一位所获得的声望，甚至比当初预想得还要大–作为2005年出版的畅销书《魔鬼经济学》(Freakonomics)的合著人，芝加哥大学(University of Chicago)的斯蒂文·列维特(Steven Levitt)如今已是家喻户晓。

“Freakonomics” owed its origins to a profile of Mr Levitt in the New York Times magazine in 2003. Its success has won a new readership for economists, beyond the business section and the opinion columns, in the glossier pages of the weekend supplements. The best young economists, as a consequence, have already attracted plenty of attention. That leaves us in a bit of a quandary. We feel like lonely prospectors, who, returning to a favourite stream, find it overtaken by a gold rush.

《魔鬼经济学》的起点是《纽约时报杂志》(New York Times magazine)在2003年对列维特先生的一个简介。它的成功，为经济学家在商业板块与意见专栏之外的版面更加活泼多彩的周末增刊里，赢得了一个新的读者群体。其结果是，那些最优秀的年轻经济学家吸引了大量的关注。这使我们有点不知所措。其感觉就像一个孤独的寻矿人，在回到一条自己钟爱的小溪旁时，却发现那里赶上了一场淘金狂潮。

Undeterred, we have given the prospecting pan another shake. We asked leading authorities in the discipline to name the best young economists in the world. Between them, they proposed over 50 researchers, but several names recurred on many lists. We have sifted the 50 down to eight, all of whom received their PhDs in the past ten years.

然而，我们并未气馁，而是做了一次更加细致的筛选。我们让该领域的重要权威们点出了当今世上最优秀的经济学后生。其中，被提名的研究者共有50多人，但是有一些名字重复出现在了名单上面。经过筛选，我们得到最终的8位入选者，他们都在过去10年获得了自己的博士学位。

The family tree
同出一门

Several of the scholars in this year’s batch trace their intellectual ancestry back to those we picked ten years ago. For example, Jesse Shapiro of the University of Chicago and Roland Fryer of Harvard are recognisably the intellectual heirs of Mr Levitt. They share the same knack for finding ingenious ways to answer unlikely questions, often by plundering forgotten troves of data.

在今年的这一组经济学家中，有几个人的学术族系可以追溯到我们在10年前所挑选的一些人身上。例如，芝加哥大学的耶希·夏皮罗（Jesse Shapiro）与哈佛的罗兰·弗莱尔（Roland Fryer）就是列维特先生公认的学术继承人。他们运用同样的技巧来为一些不太可能的问题寻找颇富创造性的答案–大多情况下是通过发掘一些被遗忘的数据宝藏。

At just 29, Mr Shapiro can already boast a collection of eye-catching findings worthy of a sequel to “Freakonomics”. He has shown that some judgments are best made without too much information: people are better at predicting the winner of American gubernatorial elections when they watch the candidates with the sound turned off. Harsher jail conditions do nothing to deter prisoners from reoffending. If anything they encourage recidivism. Preschoolers who watch television do better academically than children who don’t, especially if their parents have little education or poor English.

虽年仅29岁，夏皮罗先生已经可以因其一系列引人注目的发现而自豪，而这些发现堪称《魔鬼经济学》的续篇。他已经向人说明，不完全信息反而可以提高判断的准确性[10]。如果人们可以无声地观看美国的州长竞选者（的辩论），他们就可以更好的预测选举结果[9]。更加严苛的监狱条件对阻止犯人再犯可谓无济于事。如果非要有什么影响，就是他们会鼓励惯犯现象。那些看电视的学龄前儿童会在学业上比不看电视的孩子表现得更好，尤其当他们的父母几乎未受教育或者英语很差的时候。

Mr Fryer’s ambition is to unravel the causes of black underachievement in America, especially in education. His search for explanations extends beyond racism and poverty to contemplate the role of a self-defeating culture. He calculates that a black student who earns straight A grades will have 1.5 fewer friends from his ethnic group than an equally swotty white student.

弗莱尔先生的目标则在于解开导致美国黑人成绩不良–尤其在教育方面–的原因。他对该解释的研究跨越了种族偏见与贫困的樊篱，而把焦点放在了所谓自我挫败文化的角色上。根据他的计算，全A的黑人学生在相同种族群落中的朋友数量要比同样刻苦的白人学生少1.5个。

Michael Kremer, another of those we cited ten years ago, can also claim an intellectual relative in this year’s cohort. Esther Duflo of the Massachusetts Institute of Technology (MIT) received more recommendations than any other economist. Some who didn’t nominate her thought she was too established to count as “new”.

麦克尔·克雷默（Michael Kremer）–另一个我们在10前所褒奖过的经济学家–同样可以在今年的这一组人中找出自己学术衣钵的继承人。在推荐数量上，麻省理工学院（MIT）的埃丝特•迪弗洛（Esther Duflo）无人可出其右。而一些没有对其进行提名的人所给的理由是：她已经如此备受公认，以至于不能算作”新星”。

With her colleague, Abhijit Banerjee, Ms Duflo and Mr Kremer have remade development economics, nudging it away from its concern with policies, towards a preoccupation with projects. They study economic development as seen from the field, clinic or school, rather than the finance ministry. They might be called the “peace corps” of economists, bringing the blessing of their investigative technique to the neglected villages of India or the denuded farms of western Kenya.

协同其同事Abhijit Banerjee，迪弗洛与克雷默重塑了发展经济学，使这门学科摆脱了对政策的关心，而转向对（扶贫）项目的密切关注。他们研究经济发展的出发点是田地、诊所或者学校，而不是财政部。有人称他们是经济学家的”和平队”，把其调查技术的福祉带到了印度那些被忽略的农庄或者肯尼亚西部的荒芜农场。

Ms Duflo has made her name carrying out randomised trials of development projects, such as fertiliser subsidies and school recruitment. In these trials, people are randomly assigned to a “treatment” group, which benefits from the project, and a “control” group, which does not. By comparing the average outcome of each group, she can establish whether the project worked and precisely how well.

迪弗洛女士因为对发展项目–类似化肥补贴以及学校招聘–进行随机检验而出了名。在此类检验中，人们被随机地指派给一个”治疗”小组（该项目的受益者）以及一个”对照”小组（不是受益者）。通过对比每个小组的平均结果，她可以确定这个项目是否有效，并且有效到什么程度。

In one study, Ms Duflo and her colleagues showed that mothers in the Indian state of Rajasthan are three times as likely to have their children vaccinated if they are rewarded with a kilogram of daal (lentils) at the immunisation camp. The result is useful to aid workers, but puzzling to economists: why should such a modest incentive (worth less than 50 cents) make such a big difference? Immunisation can save a child’s life; a bag of lentils should not sway the mother’s decision either way.

迪弗洛女士与其同事的一项调查表明：在印度的拉贾斯坦邦，如果在接种站提供一公斤的小扁豆，当地母亲令其子女接种疫苗的可能性会是原来的三倍。该结果对援助人员相当有益，却令经济学家感到疑惑：为什么这么一点点激励（价值不足5毛钱）会导致这么大的不同？接种疫苗可以挽救一个孩子的生命；一袋小扁豆不该动摇母亲的任何决定。

Randomised trials “give you the chance to be surprised”, Ms Duflo says. Had they arrived at this result using some other method, she and her colleagues would have assumed they had made a mistake. But randomisation removes such doubts, showing that it was indeed the lentils that made the difference. The result cannot be dismissed; it must be explained.

正如迪弗洛女士所言，随机检验”给了你一个接受震惊的机会”。如果他们是采用其他方法得到这样的结果，她和她的同事可能还会认为是自己搞错了。然而随机化消除了这种疑虑，它表明的确是这些小扁豆造成了差异。人们不能轻视这样的结论，它必须得到诠释。

The approach has its critics. A randomised trial can prove that a remedy works, without necessarily showing why. It may not do much to illuminate the mechanism between the lever the experimenters pull and the results they measure. This makes it harder to predict how other people would respond to the remedy or how the same people would respond to an alternative. And even if the trial works on average, that does not mean it will work for any particular individual.

该方法也遭到了批评。一个随机检验可以证明一种解决方法起作用，却不必说明其原因。这意味着，对于阐释试验者的操作与其检验结果之间的这一机制，这个方法的作用不大。这增加了人们在预测他人对该方法的反应或者相同个体会对替代方案作何反应时的难度。即便这种检验平均上讲是有用的，也并不意味着他对一些特殊的具体状况同样适用。

The randomistas, as Ms Duflo and her comrades are called, liken their studies to the clinical trials that prove the efficacy of new drugs. But the ultimate ambition of economics is for something more akin to anatomy. Researchers hope to dissect the underlying physiology of an economic problem, revealing how the leg bone is connected to the thigh bone. With a full anatomy of behaviour-what economists call a structural model-they can determine if a policy or project will work even before it has been attempted.

随机统计学家–正如迪佛洛女士及她的同事被人称呼的那样–把他们的研究比作证明新药效用的临床试验。但是，经济学所最终渴望的更像是解剖一类的东西。就像揭露腿骨是如何与股骨连接在一块儿的那样，研究者们希望了解一个经济问题潜在的生理机制。凭借对某行为的完整解剖–经济学家称之为结构性模型–他们甚至可以在实施之前就确定一项政策或者一个项目是否有效。

The early anatomists of the human body suffered from a shortage of fresh cadavers to work on. Medical students would trek long distances to watch a dissection performed. Economists often find themselves in a similar predicament. Short of good empirical meat, they have to rely on elaborate theory and guesswork to fill in what they cannot observe.

早期的人体解剖学家苦于没有足够的新鲜尸体用来研究。医学院的学生为了参观一次解剖执行可能需要长途跋涉。经济学家发现他们经常处于同样的困境。因为缺乏用于实证分析的优良数据，他们不得不依赖复杂的理论以及猜测去填补那些他们无法观察的东西。

Illustration by Otto Dettmer

Amy Finkelstein, also of MIT, the fourth of our young stars, has anatomised the market for annuities in Britain. The industry suffers from “asymmetric information”: customers may know more than the provider about their chances of dying. Unfortunately, this private information is as hidden from economists as it is from the annuity company. Ms Finkelstein and a colleague, James Poterba, have shown how to infer the cost of this unseen problem from what can be observed, namely the kind of annuities people choose and the length of their life after retirement.

同样来自MIT的Amy Finkelstein–我们的第四位新星–则深度剖析了英国的养老金市场。该行业一直受困于”信息不对称”问题：亦即，关于他们的死亡概率，客户们要比养老金提供者知道得更多。不幸的是，经济学家获得这类私人信息的难度不亚于养老金公司。Finkelstein女士以及一位叫做James Poterba同事，展示了如何从那些可观察的现象上–即人们选择的养老金类型以及他们退休后的寿命长度–推知这些不可见问题的成本。

Like Ms Finkelstein, Raj Chetty, recently hired by Harvard from the University of California, Berkeley, is a promising young “public economist”: a student of tax and spend. He has great respect for structural models. But in a recent paper he makes the case for judicious short cuts. Often you don’t need to dissect a whole body; a few choice incisions are enough.

与Finkelstein女士类似，最近刚刚被哈佛从加州大学伯克利(University of California, Berkeley)翘走的Raj Chetty是个前途无量的”公共经济学家”：一个专攻政府税收与支出的学生。他对结构性模型敬重有加。然而在最近的一篇论文中他提出了一个明智的捷径–很多时候，你不必解剖整个身体，选择性地开两刀就足够了。

For example, he wanted to know whether policymakers should raise unemployment benefits. To answer this question, a structural model would need to specify how much a dollar is worth to a person on the dole, as compared with someone in work. It would also need to quantify the burden a job hunt imposes. This isn’t easy to find out. But Mr Chetty argues it is unnecessary.

例如，他想知道决策者是否应该增加失业救济金。为了回答这个问题，一个结构性模型将需指定：比起那些正在工作的人，一美元对于一个领取失业救济金的人究竟意味着什么。它还需要去量化寻找工作所带来的负担。查明他们并非易事。然而，Chetty先生认为并没有这个必要。

He gleans all the information he needs by looking at the time it takes unemployed people to find a new job. Unsurprisingly, they take longer when their benefits are more generous. This is usually attributed to “moral hazard”-people take less care to escape a danger, such as joblessness, if they are insured against it. But Mr Chetty shows that skewed incentives account for only 40% of the delay.

通过观察失业者找到一份新工作所需要的时间，他一点点地收集了所需信息。毫不奇怪，该时间在救济金更高的时候也更长。这经常归咎于”道德风险”–如果人们可以为某风险投保，例如失业，那么他们也就不会那么小心地去避免此类风险。但是Chetty先生的研究表明，造成这种延迟的原因只有40%可以归咎于这种所谓的不良激励。

The rest is due to what he calls a “liquidity effect”. The unemployed typically have few liquid assets to fall back on and little chance of a loan from the bank. This forces them to rush their job search. If they had savings to dip into or credit to tap, they might search with greater deliberation. This kind of dallying is, in a sense, optimal. The unemployed decide that an unhurried job search is worth the extra cost of depleted savings or heavier loan repayments.

剩余部分则因为一种被他称作”流动性效应”的东西。失业者通常拥有较少的流动性资产可以依赖，他们也几乎没有机会从银行得到贷款。这强迫他们加快寻找工作的速度。如果他们拥有可以周转一段的储蓄或者信贷条件去利用，他们寻找工作的步伐就会从容多了。在某种意义上，此类闲混是最优的。对失业者来说，为了一个从容不迫的求职而花光储蓄或者垒高债台都是值得的。

Higher benefits ease this liquidity problem. Raising benefits by $1 a week would do as much social good as raising American GDP by $290m, Mr Chetty calculates, although government loans to the unemployed might do better still.

增加救济金可以缓解这个流动性问题。根据Chetty先生的计算，就像社会公益一样，把周救济金提高1美元或将使美国的GDP提高2亿9千万美元–尽管，为失业者提供政府贷款的效果或许更好。

Twenty years ago macroeconomists dominated our list of the best young thinkers, but they are under-represented in this year’s batch. We found plenty of agreement about the three or four young macro thinkers most likely to succeed, but surprisingly little confidence that they would. One leader in the field suspected their work represented a moment of beauty, not truth. Another complained that the youngsters lacked the “vision thing” that distinguished the greats of the past.

20年前，宏观经济学家是这份最优年轻思想家名单上的主角。然而，他们在今年这一组中的表现却未如人意。我们发现，对于3到4位最可能成功的年轻宏观经济思想学家的入选并不缺乏大量的一致意见，可令人惊讶的是很难找到与此相关的信心。一位该领域的权威不无怀疑的说道，他们的工作所代表的只是昙花一现，而非事实真相[11]。另一些人则抱怨这些后生缺乏那种曾经成就其伟大前辈们的”远见”。
Ramsey revisited
再访拉姆齐

If so, perhaps they can blame the times that produced them. They came of age during the Great Moderation, a period of macroeconomic tranquillity and intellectual consensus. They are in thrall not to John Maynard Keynes, sage of the Depression, but to his Cambridge contemporary, Frank Ramsey, a precocious polymath who made his contributions in the prelapsarian 1920s. Ramsey was interested in how much of its income a nation should save so as to maximise its prosperity now and in the future. His work underpins much of modern macroeconomics, in which agents act today with an eye on tomorrow. But the framework is best suited to analysing steady accumulation, not violent cycles of speculation and liquidation. So it is not the obvious place to start to explain the world economy’s present predicament.

倘若如此，或许他们只能怪自己生不逢时。当他们成年时，偏偏赶上了”大稳定”–一个宏观经济上毫无波澜，学术分歧上逐渐统一的时代。他们虽未成为大萧条时期的圣人约翰·梅纳德·凯恩斯(John Maynard Keynes)的奴隶[1]，却深深地受制于后者的剑桥同仁，弗兰克·拉姆齐(Frank Ramsey)。这位早慧的博学家，在大萧条前的20年代做出了他的突出贡献。拉姆齐当时的兴趣在于，一个国家应该储蓄多少收入才能使其繁荣在今天以及将来得以最大化。他的工作为很多现代宏观经济学的理论打下了坚实基础，这些理论认为经济个体行动于今天同时亦着眼于明天。但是这个框架最适合用于分析的是那些静态的积累，而不是投机与清算的剧烈循环。所以它明显不是分析当下世界经济窘境的出发点。

The macroeconomist nominated most often for our list was Iván Werning of MIT. Mr Werning is an economist’s economist; an elegant theorist, whose early contributions provided streamlined proofs that other thinkers could make use of. One of Mr Werning’s ambitions is to unite Ramsey’s work with that of another elegant theorist, Sir James Mirrlees. Sir James won the Nobel prize in 1996 for exploring how best to set taxes when people can disguise their true worth from the revenue collector. Mr Werning asks the same question, but in the forward-looking, macroeconomic setting provided by Ramsey.

在我们的名单上得到提名最多的宏观经济学家是来自MIT的Iván Werning。Werning先生是一个经济学家的经济学家，一个精巧的理论学者。他早期的一些学术贡献为其他的经济思想学家提供了一些简化却效率更高的论证。Werning先生有一个目标，就是统一拉姆齐与另外一位精巧的理论家詹姆斯·米尔利斯爵士（Sir James Mirrlees）的工作成果。因其探讨了当人们可以向政府隐瞒真实收入时的最优税率问题，詹姆斯爵士在1996年获得了诺贝尔经济学奖。Werning先生问的是同样的问题，不过是在一个由拉姆齐所提供的具有前瞻性的宏观经济框架中。

Mr Werning and his co-authors have so far derived at least two theoretical results of note. The first is to show that the unemployed have sufficient incentive to find work, even if they receive unemployment benefits indefinitely. The second is that bequests from one generation to the next should be subsidised by the government, with smaller inheritances receiving higher rates of subsidy. Mr Werning and his co-author, Emmanuel Farhi (a young Harvard macroeconomist), point out that the biggest roll of the dice in life is the family you are born into. Their system of subsidies would take the edge off this uncertainty.

迄今，Werning先生与他的合著者已经至少得到了两个令人瞩目的理论结果。第一是表明失业者拥有足够的动机去找到工作，即便他们可以无限期的获得失业救济金。第二是世代之间的遗赠应该得到政府的补贴–即遗赠越小，补贴率就应更高。Werning先生和他的合著者，Emmanuel Farhi（哈佛大学年轻的宏观经济学家）指出，人生中最大的赌博就是你所出生的家庭。他们补贴体系或将减弱这种不确定性。

Two of the economists we highlighted ten years ago-David Laibson of Harvard and Matthew Rabin of Berkeley-were exponents of “behavioural economics”, incorporating the insights of psychology into the dismal science. The sub-discipline has continued to flourish in the decade since, seeping so far into the mainstream that its disciples no longer constitute a self-contained school. The randomistas, for example, often invoke behavioural explanations for their experimental results.

我们在10年前高亮的两位经济学家–哈佛大学的David Laibson和加州伯克利的Matthew Rabin–是”行为经济学”的倡导者，这项把心理学的深刻洞察融入到沉闷科学[3]的理论分支，在最近的10年中得以继续繁荣发展，并至此渗入到了主流经济学之中。如今，经济学的信徒已经不再组建自我独立的学派。例如，那些随机统计学家就经常援引行为学的观点来解释其实证检验的结果。

Xavier Gabaix of New York University, our seventh pick, is another example of someone who is au fait with behavioural economics but not defined by it. He has written papers with Mr Laibson, including one that explains why hotels can get away with overpricing the mini-bar. But his interests extend beyond the behavioural.

纽约大学的Xavier Gabaix–我们的第7位入选者–便是精通行为经济学却并不受其局限的一个代表。他已经和Laibson先生一同撰写了几篇论文，其中一篇对旅馆里定价过高的微型酒吧为什么可以侥幸得手提供了解释[2]。然而他的兴趣超越了行为学的范畴。

He has, for example, shown a fascination with “power laws”: tantalising statistical patterns that seem to crop up wherever you look hard enough. The size of cities, the pay of executives and the performance of the stockmarket all seem to follow such laws. For cities, the law can be crudely expressed as the “rank-size rule”. The second-biggest city will have roughly half the population of the biggest; the population of the third-ranked city will be one-third of the first’s, and so on. The relationship between executive pay and company size also obeys a power law: companies twice the size tend to pay their chief executives roughly 25% more.

例如，他向人们展示了”幂定律”[4]的魅力。这是一种令人迷惑的、似乎通过足够仔细地观察处处都会出现的统计形态。城市规模，高管薪酬以及股市表现看上去都遵行这一定律。对城市而言，该定律可粗略地表达为”顺位规模法则”[5]。第二大城市的人口规模大概只有第一大城市的一半；而第三大城市的人口就只有第一大的三分之一，以此类推。高管报酬与其公司规模同样遵行幂数定律：一个相对具有双倍规模的公司付给其高管的薪酬大概也多出25%。

These curious regularities have more than numerological appeal. They give clues about what can and cannot explain the size and growth of the things they describe. For example, the rank-size rule could not hold if small cities grew systematically faster than big ones, or vice versa. The power law of executive pay also requires a particular kind of economics to explain it. Mr Gabaix thinks the “economics of superstars”,[6] invented by Sherwin Rosen, fits the bill.

这些奇妙规律的感染力并不局限于数字命理的范畴。在解释所描述对象的规模和增长问题时，他们为方法上的优势和局限提供了线索。例如，当小城市的发展速度整体上超过了大城市，那么顺位规模法则就难以成立。高管薪酬幂定律的成立同样要求在一个特定的经济环境中加以解释。Gabaix先生认为由Sherwin Rosen所开创的”超级明星经济学”满足了这一要求。

Illustration by Otto Dettmer

Top executives may differ only slightly in their talents, just as sports champions differ only slightly from runners-up. But the better managers nonetheless get hired by the bigger firms, just as the best entertainers sing to the largest audience. This means an executive’s small edge in managerial skill is amplified, because his talents go to work on a bigger canvas. Mr Gabaix made a splash in 2006 when he concluded that the “excessive” pay of chief executives was not necessarily excessive. Compensation may have grown sixfold from 1980 to 2003 not because managers were six times greedier, but because the firms they ran were six times bigger.

正如体坛冠军只是略胜于其亚军，顶级经理人在才能之间的差异也是微乎其微。然而，正如最好的艺人为最广大的观众演出一般，更好的管理者往往受佣于更大的公司。这意味着一个高级经理在管理技能上的微弱优势得到了放大，因为他可以在一个更宽广的舞台发挥自己的才能。当Gabaix先生在2006年得出结论，认为高管薪酬”过高”未必真的过分时，他掀起了一阵波澜。高管的薪酬水平从1998年到2003年间涨了6倍，或许并非因为高管的贪欲、而是公司的规模放大了6倍。

If the size of firms obeys a power law, economies will comprise some very big firms and a long tail of small ones. The fortunes of the biggest companies might then stir the whole economy, Mr Gabaix conjectures. The $24 billion dividend paid by Microsoft in December 2004, for example, added 3% to America’s personal income that month. Mr Gabaix calls for a more “granular” approach to macroeconomics, which would weigh the contribution of big firms to national aggregates.

倘若公司规模遵循幂定律，那么许多经济的样子就是一些非常大公司加上一个由众多小公司所构成的”长尾”[7]。Gabaix先生猜想，那些最大的公司的命运或将影响整个经济。例如，微软公司在2004年12月的分红，一下子让美国的人均收入在当月提高了3个百分点。Gabaix先生呼吁一个更加”粒状”的宏观经济研究方法，以便可以衡量大公司对整个国民经济总和的贡献。

This granular view is already taking hold in studies of international trade. Countries, after all, do not trade with each other; companies do. A few firms usually account for the lion’s share of a country’s exports: in America, the top 10% of exporters account for 96% of the country’s foreign sales, and only 4% of firms export at all.

这种粒状的思考方式已经在国际贸易的研究中生根发芽。毕竟，不是每个国家之间都会有贸易往来，公司也是如此。通常，很少的几家公司就占了一国出口的最大份额。在美国的出口企业中，最顶尖的那10%占到了整个国家海外销售总额的96%；而在全部的企业中，只有4%出口自己的产品。

These observations (drawn from work by Andrew Bernard of Dartmouth College among others) demand a theory to explain them. That gap has been filled by Marc Melitz, a trade economist at Princeton University and our final new star.

这些观察数据（源自达特茅斯学院(Dartmouth College)的Andrew Bernard及其他一些人的工作）需要一个理论来解释。我们的最后一位新星，普林斯顿大学的贸易经济学家Marc Melitz填补了这个空白，

Mr Melitz is a pioneer of the “new, new trade theory”, which succeeds the “new” trade theory propounded by Mr Krugman almost 30 years ago. The source of its novelty is its recognition that firms differ, and only the best firms export. In America, for example, exporting factories are more than twice as big as plants that do not sell beyond their shores, and they squeeze 14% more out of their workers.

Melitz先生是”新新贸易理论”–作为克鲁格曼先生在将近30年前提出的”新”贸易理论的下一代理论模型–的研究先锋。之所以”新”是因为它识别了公司间的不同，而只有那么最好的公司才会出口。例如，在美国，出口型工厂要比那些只在国内销售的工厂规模大出两倍有余。此外，他们还能从其雇员身上多榨出14%的产值。

In Mr Melitz’s theory firms first prove themselves at home, discovering their own limits and abilities. Only the best then venture overseas. Entering a foreign market is an expensive endeavour, he points out, even before firms encounter the tariffs or transport costs that preoccupy most trade models. An exporter must find and introduce itself to distant customers, comply with alien regulations and set up distribution channels abroad. One study found that it cost Colombian chemical factories over $1m to enter a foreign market.

在Merlitz先生的理论中，公司首先要在家里证明自己的能力：了解他们自己的局限与优势。之后，只有那些最好的才会到海外去冒险。他指出，即便在考虑大多数贸易模型所关注的关税与运输成本之前，进入海外市场的努力也是相当昂贵的。向外出口的公司必须找到那些遥远的客户并让他们了解自己，还要遵从陌生的监管法则并在国外建立自己的销售渠道。一项研究发现，为进入一个海外市场，哥伦比亚的化工厂要付出超过1百万美元的代价。

The gains from trade also differ in Mr Melitz’s model. In the new trade theory that preceded it, international commerce raises the productivity of firms by enlarging their market, allowing them to reap economies of scale. In Mr Melitz’s model, trade raises the productivity of industries, not by allowing firms to grow bigger, but by giving the better firms a bigger share of the market. Foreign competition sifts and sorts firms, winnowing out the weakest firms and leaving a greater share of the market to their stronger rivals.

在Melitz先生的模型中，贸易的好处也略有不同。在其之前的新贸易理论中，公司通过扩大市场而在国际商业活动中提高了自己的生产率，从而允许他们获得规模效益。在Melitz先生的模型中，贸易提高产业生产率的原因并非是其使公司变大，而是因为它让较好的公司获得了更大的市场份额。海外竞争将公司进行筛选并分类，扬弃了那些最弱的公司，而把更大的市场份额留给他们更强大的竞争对手。

Just as Mr Krugman found a clean way to account for economies of scale, Mr Melitz handles the heterogeneity of firms without spoiling the lines of his model. It now serves as a pliant workhorse for lots of “granular” thinking in the field.

正如克鲁格曼先生了找到了一个简洁方法来解释规模效益，Melitz先生在不破坏其模型结构的情况下处理了公司之间的异质性。如今在该领域的许多”粒状”研究中，这一方法可谓百试不爽。

Bodice rippers
冲破束缚

Over 60 years ago Paul Samuelson laid down “the foundations of economic analysis” in his seminal work of that name. In the introduction, he describes his dawning realisation of the underlying unity of the subject. As he laboured in each field-consumer behaviour, public finance, international trade, business cycles-he encountered similar problems, which yielded to the same set of mathematical techniques. Mr Samuelson’s book squeezed a shapeless body of economic knowledge into a tight corset.

60余年前，保罗·萨缪尔森在一篇同名的开创性著作中奠定了”经济分析的基础”。在序言中，他描述了自己对该学科潜在统一的初始体会。当他在各领域–包括消费者行为、财政学、国际贸易、商业周期–辛勤耕耘时，总是遭遇到一些类似的、屈从于数学技巧的同一局限的问题。萨缪尔森先生的这本书成了一件约束经济学知识这个无形躯体的紧身衣。

In the decades since, the laces have been unpicked. It is not just that economists are nosing into new fields of social behaviour. They have been doing that at least since Gary Becker of the University of Chicago wrote about crime and the family in the 1960s and 1970s. But today’s economists show no great attachment to the rational model of behaviour that guided Mr Becker. Economic theory has become so eclectic that ingenious researchers can usually cook up a plausible model to explain whatever empirical results they find interesting. Economics is now defined neither by its subject matter nor by its method.

自那以后的几十年来，这种束缚得以松绑。其原因并不仅在于经济学家们正在探究社会行为中一些新领域。至少从芝加哥大学的加里·贝克在上世纪60和70年代用经济学解释犯罪与家庭行为以来，他们就已经在做这样的事情。但是今天的经济学家并未对贝克先生所引导的理性行为模型表现出非同寻常的依赖。经济学理论已经变得如此包容，以至于富于创造性的研究者经常可以编出一个令人信服的模型来解释他们所感兴趣的任何实证检验的结果。如今定义经济学的既不是他的研究课题也不是他的研究方法。

What, then, unites these eight young stars and the discipline they may come to dominate? Economists still share a taste for the Greek alphabet: they like to provide formal, algebraic accounts of the behaviour they explain. And they pride themselves on the sophistication of their investigative methods. They are usually better at teasing confessions out of data than their rivals in other social sciences. What defines economics? Economics is what economists do-the best of them, anyway.

那么，究竟是什么使这8位新星以及他们或将统治的研究领域得以统一呢？经济学家们始终有一个对希腊字母的共同嗜好：他们喜欢为他们解释行为的理由提供严谨的数学证明，并且为这些复杂的研究方法而自豪。与社会科学中的其他对手相比，他们往往更擅长从数据中梳理出隐藏的原因。该如何定义经济学呢？其实经济学就是经济学家所做的东西[8]–至少是那些最好的经济学家。

==================================

[注释]

[1] 这有个小典故，凯恩斯曾经有句很著名的话：”经济学家与政治哲学家的思想，无论对与错，都比我们通常所理解的要强大得多。的确，世界掌握在少数人手中。那些深信自己不受任何空谈家影响的务实主义者，却往往俯首成为一些已故经济学家的奴隶。” ，这里的”奴隶”也是这么来的。

[2] 相关文章见： http://www.nytimes.com/2006/12/10/magazine/10Section2a.t-3.html

[3] the dismal science 对经济学的一种讽刺说法

[4] 幂定律：[http://en.wikipedia.org/wiki/Power_law]

[5] 顺位规模法则：城市地理研究的一种定量化理论与方法。它反映世界各地区城市人口规模与按城市人口规模大小的顺序数之间的数量关系，其数学模式为：PI=R/RI (R为区域内最大城市人口数;RI为第I个城市的顺次编码号I是第I城市的人口数;城市地理研究中应用顺位–规模法则分析区域城镇群结构,预测城市 规模的变化趋势.

[6] 根据经济学家舍温•罗森（Sherwin Rosen）早期论述”超级明星”效应的一篇论文，运动场上，只有少数顶级选手能够脱颖而出。作者对篮球运动员一年挣120万美元或电视明星一年挣200万美元表达了愤怒。并最终找到了真相：根据罗森的观点，这种不平均来自一种竞赛效应：某个稍稍”优秀”一点的人能够轻易赢得整块蛋糕，使其他人什么也得不到。人们宁意花10.99美元购买霍洛维茨的音乐，也不愿意花 9.99美元购买某个挣扎中的钢琴家的音乐。即认为技能是成功的核心因素。随机事件或者意外事件也可以解释成功，并且成为赢者全赢结果的原动力。一个人可能完全因为随机的原因而稍稍领先其他人；由于我们喜欢互相模仿，我们会蜂拥而上地模仿他。传染病的世界是如此被低估！这一学派的思路简而概之，就是：热门产品会继续大卖，而冷门产品越来越冷清。”[http://www.yeeyan.com/articles/source/50529_a03/The_Economics_of_Superstars%EF%BC%88%22%3B%E8%B6%85%E7%BA%A7%E6%98%8E%E6%98%9F%E6%95%88%E5%BA%94%22%3B%E7%BB%8F%E6%B5%8E%E5%AD%A6%E8%AE%BA…]

关于”超级明星经济学”的入门读物，请参见：
[http://www.geocities.com/valencia_aaup/The_Economics_of_Superstars.html]

[7] “长尾”（The Long Tail）这一概念是由美国连线（Wired）杂志主编克里斯·安德森（Chris Anderson）在2004年提出的，它实际上是统计学中”指数律”（Power Laws）和帕累托（Pareto）分布特征的口语化表达。它生动而形象地反映了我们的经济和文化正在从为数较少的主流产品和市场（头部），向数量众多的 狭窄市场（尾部）转移的现象。
长尾理论的提出很大程度上是源于互联网的普及和互联网行业的欣欣向荣，其基本原理是：只要存储和流通的渠道足够大，需求不旺或销量不佳的产品所共同占据的市场份额可以和那些少数热销产品所占据的市场份额相匹敌甚至有过之而无不及。可见畅销财经书刊 《长尾理论》
[http://www.gemag.com.cn/geblog/User0/124/Show.asp?/_articleid/361.html]

[8] 传说此话出自加拿大籍经济学家 Jacob Viner.
[http://forum.quoteland.com/1/OpenTopic?a=tpc&s=586192041&f=099191541&m=723190963]

[9] 证明天真是进行良好预测的一个很重要的条件。论文见 [http://www.nber.org/papers/w12660.pdf]

[10] 考虑到微观经济学的两个基本假设 1. 完全理性人假设 .2. 完全信息假设。夏皮罗的发现在某种意义上至少对第二点提出了质疑。感谢西牟兄（Simurgh）指点。

[11] 这里又涉及到宏观经济学研究上的问题。《高级宏观经学》的作者David Romer曾经说，我们不需要制造完全真实的模型，因为我们已经有了，而那就是现实世界本身。对于宏观经济学来说，用相对简单的数学模型来描述复杂多变的宏观经济问题是很elegant的事情–他们的很多模型也的确处理得非常非常漂亮（至少在数学上）–然而这也是他们备受批评之处，因为简化的模型无法真实反映现实的世界。再次感谢西牟兄！

译者：弓长贝恩          http://www.ecocn.org/bbs/viewthread.php?tid=16386&extra=&page=1