Should We Trust Economists？ 經(jīng)濟(jì)學(xué)家可信嗎？

Imagine you are the Royal Physician of England some time during the 14th century. The prince is sick， and youve been summoned to help. You call in two experts for advice. The first says： “Use leeches1） to suck out the evil humors2）.” The second says： “No， you must bleed him to get the evil humors out.” They start to argue， insulting each other in nasty epistles3）. “Leech guy is secretly working for the French！” alleges Bleeding Guy. “Bleeding Guy just wants the prince to die because the prince wanted higher taxes on the nobles！” Leech Guy fires back.

Whats the right move？ Well， in an ideal world， you would go and get 999 patients who have illnesses similar to the princes and give them all a variety of household substances， such as bread mold4）. Then you would take careful note of who died and use statistical analysis to figure out which household substances cured disease. Thus， you would discover penicillin5） and invent modern medicine.

Sadly， this is not what you do， because a） if you proposed it， you would be led off to the dungeons6） and beheaded b） its the 14th century and you have no concept of the scientific method and c） you dont really have the right tools for that experiment， anyway. Instead， its bleeding or leeches. So you take your best guess and you pray youre right.

The economic situation we find ourselves in today is a little bit like the example above. Everyone knows that its a bad thing when factories sit gathering dust and potential workers sit idle on their couches. But the best “experts” that we have—academic economists—are in generally ill repute. Surveys have shown that the public has very little confidence in their predictions. They argue bitterly on op-ed pages7） and cant seem to agree on the most basic issues. So are we making a mistake putting our faith in economics？ Are economists themselves just charlatans8）， to be scorned as medieval cranks9）？ Or for all10） their flaws， are they really the best experts we have？ I dont have a definitive answer， just like there is no good answer to the problem of the Royal Physician. But having gone through an economics PhD， I do know a few things that I think the public should realize about the field.

To start， we need to talk briefly about what it is economic theorists do. Essentially， they make models， which are mathematical tools that are supposed to describe how the economy functions. The problem is that economists havent really built a model of the whole economy that works. A lot of smart people have spent a lot of time creating tools with names like “dynamic stochastic general equilibrium11）.” But as of this moment， those models cant really forecast the economy like our meteorologists12） can forecast the weather. Furthermore， they contain a lot of obviously wrong assumptions. To give just one example， many of the models stipulate13） that companies are only allowed to change their prices at random times！ Crazy， right？ Economists include things like that to make the models easier to use， and they hope that those zany14） assumptions are actually decent approximations to the way the world really works. But even with these kludges15） in place， none of the existing models can do much to predict the economy.

Theory isnt the only problem. Economists dont really have good enough data to understand how the economy works， either. With chemistry or biology， you can put things in a lab and test them out with controlled experiments. With microeconomics—the study of specific markets—you can do something similar. But with macroeconomics—the study of the economy as a whole—you cant put countries and entire economies in a lab； all you can do is sit there and watch history go by， and try to deduce some patterns. But often enough， those patterns vanish just as soon as you think youve found one.

Just as it doesnt have their caliber16） of data， macroeconomics also lacks the kind of scientific culture enjoyed by biology and chemistry. In the hard sciences17）， models are built to explain data； thats their only purpose. But in econ， models are often used simply as storytelling devices to explain an idea about how the world might work.

The best economists are well aware of their ignorance. During his recent graduation speech at Princeton， Federal Reserve Chairman Ben Bernanke18） half-joked to the crowd that “Economics is a highly sophisticated field of thought that is superb at explaining to policymakers precisely why the choices they made in the past were wrong. About the future， not so much.” Greg Mankiw19）， one of the worlds most famous macroeconomists put the sentiment this way in a 2011 New York Times column：

“After more than a quarter-century as a professional economist， I have a confession to make： There is a lot I dont know about the economy. Indeed， the area of economics where I have devoted most of my energy and attention—the ups and downs of the business cycle—is where I find myself most often confronting important questions without obvious answers ...”

What all this means is that when an economist tells you something that is based on a theory or a model， you should be very， very skeptical. And the more complicated the theory or model is， the more you should be suspicious. Beware of economists bearing fancy models.

If economists ever do succeed in developing formal models that work better， then well be able to go to them with questions （like “Should the Fed print more money？”） and simply trust their expert advice. But until that day， all economists can really give us is intuition， suggestions， and ideas. Like the Royal Physician， each of us then has to decide for him/herself what we think is the best medicine. So when you listen to economists， the key is to try to understand why they think what they think. For example， Paul Krugman20） thinks that monetary policy doesnt work well in a depression， because nominal interest rates21） cant go below zero， and because the Fed is not always good at convincing people that it will allow inflation in the future. Robert Barro22） thinks that fiscal policy doesnt work， because people anticipate the future taxes needed to pay for todays stimulus， and reduce their consumption today in order to save up to pay those future taxes. Most people can understand these basic ideas， and decide for themselves which they think are plausible， and which they think are unrealistic.

Economists have another virtue， in that theyre very good at pointing out each others logical errors. On the whole， economists are very smart， perceptive people. Like everyone else， they are liable to overstate their confidence and rely too much on their own unproven theories. But when they do this， other economists usually catch them！ So in order to avoid believing too much in the confident-sounding pontifications23） of one economist， you should listen to economists on the other side of the issue.

No matter how much we might wish they were， economists are not go-to24） experts who know just how the world works or how to fine tune it. They are not car mechanics. And if they act like they are car mechanics， you should instantly be suspicious. But they do have a lot of interesting things to say. They might help you clarify or re-evaluate your own beliefs about how the economy functions. They can also help you spot the flaws in each others arguments.

And in the end， youre the Royal Physician. You may not know everything， but the prince is dying， and you pick from among the “experts” youve got.

想象一下，假如你是14世紀(jì)某個(gè)時(shí)期的英格蘭皇家御醫(yī)。王子生病了，你應(yīng)召來救助。你請(qǐng)來兩位專家提供建議。第一位說：“用水蛭把有害的體液吸出來?！钡诙€(gè)說：“不行，你必須得給他放血，讓有害的體液排出來?！彼麄冮_始爭(zhēng)論，用惡毒的書信體詩(shī)文相互侮辱對(duì)方。放血男聲稱：“水蛭男背地里正在為法國(guó)人效力！”水蛭男回?fù)舻溃骸胺叛芯褪窍胍踝拥拿?，因?yàn)橥踝釉胍o貴族們加稅！”

正確的做法是什么？在一個(gè)理想的世界里，你會(huì)去找999個(gè)與王子患有類似疾病的病人，給他們服用各種各樣家中常見的物質(zhì)，比如面包霉。然后你會(huì)仔細(xì)記錄哪些人死亡了，并運(yùn)用統(tǒng)計(jì)分析查明哪些家中常見的物質(zhì)治愈了疾病。如此一來，你將會(huì)發(fā)現(xiàn)青霉素并發(fā)明現(xiàn)代藥物。

遺憾的是，你并沒有這樣做，原因如下：①如果你提議這樣做，就會(huì)被打入地牢并被斬首；②當(dāng)時(shí)是14世紀(jì)，你沒有科學(xué)方法的概念；③不管怎么樣，你其實(shí)并沒有用于該實(shí)驗(yàn)的合適工具。相反，要么放血，要么用水蛭。因此你做出了最合理的猜測(cè)，并祈禱自己是正確的。

現(xiàn)如今我們發(fā)現(xiàn)我們所處的經(jīng)濟(jì)形勢(shì)與上述例子有點(diǎn)兒類似。每個(gè)人都知道，當(dāng)工廠閑置攢灰而待業(yè)工人卻坐在沙發(fā)上無所事事是件糟糕的事情。但是我們最好的“專家”——學(xué)院派經(jīng)濟(jì)學(xué)家——基本上名聲不佳。調(diào)查表明，公眾對(duì)經(jīng)濟(jì)學(xué)家的預(yù)測(cè)幾乎毫無信心。他們?cè)趫?bào)紙的專欄版上激烈爭(zhēng)論，似乎在最基本的問題上都無法達(dá)成共識(shí)。那么我們信任經(jīng)濟(jì)學(xué)是不是在犯錯(cuò)誤？經(jīng)濟(jì)學(xué)家是不是就是冒充內(nèi)行的騙子，應(yīng)該像中世紀(jì)怪人那樣遭到蔑視？還是說盡管他們有缺點(diǎn)，但他們真的是我們擁有的最好的專家？我沒有一個(gè)確定的答案，就像御醫(yī)的問題也沒有令人滿意的答案一樣。但是攻讀完經(jīng)濟(jì)學(xué)博士學(xué)位后，我的確知道一些我認(rèn)為公眾對(duì)這個(gè)領(lǐng)域應(yīng)該了解的事情。

首先，我們需要簡(jiǎn)單談?wù)劷?jīng)濟(jì)理論學(xué)家是做什么的?；旧?，他們是在建立模型，而模型被認(rèn)為是用來描述經(jīng)濟(jì)如何運(yùn)行的數(shù)學(xué)工具。問題是經(jīng)濟(jì)學(xué)家還未真正地創(chuàng)建出一個(gè)有效的整體經(jīng)濟(jì)模型。很多聰明人士已經(jīng)花費(fèi)了大量時(shí)間創(chuàng)造出了名稱諸如“動(dòng)態(tài)隨機(jī)一般均衡”的工具。但截至目前，這些模型無法像我們的氣象學(xué)家預(yù)測(cè)天氣那樣真正地預(yù)測(cè)經(jīng)濟(jì)。而且這些模型包含著很多明顯錯(cuò)誤的假設(shè)。就舉一個(gè)例子吧，很多模型規(guī)定，只允許公司不定時(shí)地調(diào)價(jià)！很荒唐，是吧？經(jīng)濟(jì)學(xué)家納入這樣的假設(shè)是為了使模型更容易使用，而且他們希望這些可笑的假設(shè)其實(shí)相當(dāng)接近于世界真正的運(yùn)行方式。但是即便這些勉強(qiáng)拼湊的內(nèi)容成立，在預(yù)測(cè)經(jīng)濟(jì)方面，現(xiàn)有模型中也沒有哪個(gè)能發(fā)揮多大作用。

理論不是唯一的問題。經(jīng)濟(jì)學(xué)家其實(shí)也沒有足夠好的數(shù)據(jù)來理解經(jīng)濟(jì)是如何運(yùn)作的。對(duì)于化學(xué)或者生物學(xué)，你可以把東西放到實(shí)驗(yàn)室中，并利用可控實(shí)驗(yàn)對(duì)它們進(jìn)行測(cè)試。對(duì)于研究具體市場(chǎng)的微觀經(jīng)濟(jì)學(xué)，你可以做類似的事情。但是對(duì)于將經(jīng)濟(jì)作為整體來研究的宏觀經(jīng)濟(jì)學(xué)，你無法把國(guó)家和整個(gè)經(jīng)濟(jì)體放進(jìn)實(shí)驗(yàn)室，你能做的就只是坐看歷史變遷并試圖推斷出某些經(jīng)濟(jì)模式。但往往就在你認(rèn)為自己找到了某種模式時(shí)，它們就消失了。

正如宏觀經(jīng)濟(jì)學(xué)缺乏生物學(xué)和化學(xué)那樣的數(shù)據(jù)標(biāo)準(zhǔn)一樣，它也缺乏這兩個(gè)領(lǐng)域所享有的那種科學(xué)文化。在硬科學(xué)中，模型為了解釋數(shù)據(jù)而建，這就是它們唯一的目的。但在經(jīng)濟(jì)學(xué)中，模型往往只被當(dāng)成講故事的工具，用來解釋關(guān)于世界可能會(huì)如何運(yùn)作的某種觀點(diǎn)。

頂級(jí)的經(jīng)濟(jì)學(xué)家們十分清楚自己的無知。（美國(guó)）聯(lián)邦儲(chǔ)備局主席本·伯南克最近在普林斯頓大學(xué)發(fā)表了畢業(yè)演講，期間他對(duì)聽眾半開玩笑說：“經(jīng)濟(jì)學(xué)是一個(gè)高度復(fù)雜的思想領(lǐng)域，非常擅長(zhǎng)向決策者們清晰準(zhǔn)確地解釋他們過去的選擇為什么是錯(cuò)誤的，但對(duì)于未來，就不那么擅長(zhǎng)了?！笔澜缟献钪暮暧^經(jīng)濟(jì)學(xué)家之一格雷格·曼昆在2011年《紐約時(shí)報(bào)》的專欄中如此表述了這樣的感想：

“在當(dāng)了超過25年的職業(yè)經(jīng)濟(jì)學(xué)家后，我有件事要坦白：對(duì)于經(jīng)濟(jì)，我有很多不了解的地方。事實(shí)上，研究經(jīng)濟(jì)周期起伏的經(jīng)濟(jì)學(xué)領(lǐng)域是我投入精力最多、關(guān)注最多的領(lǐng)域，卻也是我發(fā)現(xiàn)自己最常遇到一些沒有明顯答案的重要問題的領(lǐng)域……”

所有這些都意味著，當(dāng)一位經(jīng)濟(jì)學(xué)家告訴你基于某種理論或某個(gè)模型推導(dǎo)出的事情時(shí)，你應(yīng)當(dāng)對(duì)此持強(qiáng)烈的懷疑態(tài)度。而且該理論或模型越復(fù)雜，你就越應(yīng)該感到可疑。對(duì)使用花哨模型的經(jīng)濟(jì)學(xué)家要多留神。

如果經(jīng)濟(jì)學(xué)家確實(shí)成功創(chuàng)建出了更奏效的正式模型，那么我們將能夠帶著問題去找他們（例如“美聯(lián)儲(chǔ)應(yīng)當(dāng)印更多的錢嗎？”）并完全信任他們的專家建議。但在那一天到來之前，所有經(jīng)濟(jì)學(xué)家真正能給我們的是直覺、建議和想法。就像那位皇家御醫(yī)一樣，我們每個(gè)人接下來都不得不自己確定，什么才是我們認(rèn)為最好的藥物。因而當(dāng)你聽經(jīng)濟(jì)學(xué)家講話時(shí)，關(guān)鍵是嘗試去理解他們?yōu)槭裁磿?huì)產(chǎn)生那種想法。例如，保羅·克魯格曼認(rèn)為，在經(jīng)濟(jì)蕭條期，貨幣政策的效果并不好，因?yàn)槊x利率不能降到零以下，而且因?yàn)槊缆?lián)儲(chǔ)并不總是擅長(zhǎng)說服人們相信美聯(lián)儲(chǔ)將在未來允許通貨膨脹。羅伯特·巴羅認(rèn)為財(cái)政政策沒有效果，因?yàn)槿藗冾A(yù)計(jì)今天的刺激政策需要未來的稅收來買單，于是減少當(dāng)前的消費(fèi)以儲(chǔ)備資金，用于支付這些未來的稅賦。大多數(shù)人能夠理解這些基本的想法，并自己決定哪些看法是說得過去的，哪些看法他們認(rèn)為是不現(xiàn)實(shí)的。

經(jīng)濟(jì)學(xué)家還有另一個(gè)美德，就是他們非常善于指出彼此的邏輯錯(cuò)誤。總體而言，經(jīng)濟(jì)學(xué)家們都是非常聰明、敏銳的人。就像其他所有人那樣，他們?nèi)菀走^分自信并過于依賴自己未經(jīng)證實(shí)的理論。但是當(dāng)他們這么做時(shí)，其他經(jīng)濟(jì)學(xué)家通常會(huì)逮他們個(gè)正著！因此，為了避免過分相信某位經(jīng)濟(jì)學(xué)家聽上去自信的臆斷，你應(yīng)當(dāng)聽聽在此問題上持另一種意見的經(jīng)濟(jì)學(xué)家有何觀點(diǎn)。

經(jīng)濟(jì)學(xué)家并不是知道世界如何運(yùn)轉(zhuǎn)或該如何對(duì)其進(jìn)行精細(xì)調(diào)整的關(guān)鍵專家，無論我們可能多么希望他們是這樣的人。他們不是汽車技工。如果他們像汽車技工那樣做事，你應(yīng)當(dāng)立即產(chǎn)生懷疑。但是他們的確有很多有趣的意見可以提供。他們可能會(huì)幫助你澄清或重新評(píng)估你自己關(guān)于經(jīng)濟(jì)如何運(yùn)轉(zhuǎn)的看法。他們還能夠幫助你發(fā)現(xiàn)別人論斷中的缺陷。

最終，你是那位皇家御醫(yī)。你或許并不是無所不知，但王子奄奄一息，而你得從你已有的“專家”中挑選出一位。

1. leech [li?t?] n. 水蛭，螞蟥

2. humor [?hju?m?（r）] n. （中世紀(jì)生理學(xué)中所稱對(duì)人的健康和性情起決定作用的）體液

3. epistle [??p?sl] n. 書信體詩(shī)文

4. bread mold：[微]面包霉（通常指出現(xiàn)在霉面包等上的黑根霉）

5. penicillin [?pen??s?l?n] n. [藥]青霉素

6. dungeon [?d?nd??n] n. 地牢

7. op-ed page：〈美〉（報(bào)紙的）專欄版，特寫稿版（由專欄作者等署名撰文，與社論版相對(duì)）

8. charlatan [??ɑ?l?t?n] n. 假裝內(nèi)行的人；冒充者；騙子

9. crank [kr??k] n. 怪人

10. for all：雖然，盡管

11. dynamic stochastic general equilibrium：動(dòng)態(tài)隨機(jī)一般均衡，該模型是目前貨幣政策分析與經(jīng)濟(jì)預(yù)測(cè)的重要工具。

12. meteorologist [?mi?ti??r?l?d??st] n. 氣象學(xué)家

13. stipulate [?st?pjule?t] vt. 規(guī)定

14. zany [?ze?ni] adj. 滑稽的；愚蠢的

15. kludge [klu?d?] n. 為某個(gè)目的而勉強(qiáng)拼湊的內(nèi)容

16. caliber [?k?l?b?（r）] n. 水準(zhǔn)，質(zhì)量

17. hard science：硬科學(xué)，自然科學(xué)與技術(shù)科學(xué)兩大系統(tǒng)所有學(xué)科與其交叉學(xué)科的統(tǒng)稱，借用電子計(jì)算機(jī)的“硬件”而得名。研究領(lǐng)域包括數(shù)學(xué)、物理學(xué)、化學(xué)、天文學(xué)、地理學(xué)、生物科學(xué)以及技術(shù)工程等學(xué)科。

18. Ben Bernanke：本·伯南克（1953～），美國(guó)經(jīng)濟(jì)學(xué)家，現(xiàn)任美國(guó)聯(lián)邦儲(chǔ)備局（簡(jiǎn)稱“美聯(lián)儲(chǔ)”）主席。

19. Greg Mankiw：格雷格·曼昆（1958～），美國(guó)著名經(jīng)濟(jì)學(xué)家，29歲成為哈佛大學(xué)歷史上最年輕的終身教授之一，2003年走入政壇，著有《經(jīng)濟(jì)學(xué)原理》、《宏觀經(jīng)濟(jì)學(xué)》等經(jīng)典教材。

20. Paul Krugman：保羅·克魯格曼（1953～），美國(guó)經(jīng)濟(jì)學(xué)家，自由經(jīng)濟(jì)學(xué)派的新生代，理論研究領(lǐng)域是貿(mào)易模式和區(qū)域經(jīng)濟(jì)活動(dòng)，2008年獲諾貝爾經(jīng)濟(jì)學(xué)獎(jiǎng)。

21. nominal interest rate：名義利率，是央行或其他提供資金借貸的機(jī)構(gòu)所公布的未調(diào)整通貨膨脹因素的利率，即利息（報(bào)酬）的貨幣額與本金的貨幣額的比率。

22. Robert Barro：羅伯特·巴羅（1944～），當(dāng)今世界最具影響力的經(jīng)濟(jì)學(xué)家之一，凱恩斯經(jīng)濟(jì)學(xué)的代表人物，由于他在宏觀經(jīng)濟(jì)學(xué)、經(jīng)濟(jì)增長(zhǎng)、貨幣理論與政策等領(lǐng)域所做出的卓越貢獻(xiàn)，被推選為美國(guó)藝術(shù)與科學(xué)學(xué)院院士。

23. pontification [?p?nt?f??ke??（?）n] n. 自負(fù)的言論，武斷的話

24. go-to：關(guān)鍵的，靈魂的