Should We Trust Economists？ 經濟學家可信嗎？

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世紀某個時期的英格蘭皇家御醫。王子生病了，你應召來救助。你請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€說：“不行，你必須得給他放血，讓有害的體液排出來?！彼麄冮_始爭論，用惡毒的書信體詩文相互侮辱對方。放血男聲稱：“水蛭男背地里正在為法國人效力！”水蛭男回擊道：“放血男就是想要王子的命，因為王子曾想要給貴族們加稅！”

正確的做法是什么？在一個理想的世界里，你會去找999個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，比如面包霉。然后你會仔細記錄哪些人死亡了，并運用統計分析查明哪些家中常見的物質治愈了疾病。如此一來，你將會發現青霉素并發明現代藥物。

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

現如今我們發現我們所處的經濟形勢與上述例子有點兒類似。每個人都知道，當工廠閑置攢灰而待業工人卻坐在沙發上無所事事是件糟糕的事情。但是我們最好的“專家”——學院派經濟學家——基本上名聲不佳。調查表明，公眾對經濟學家的預測幾乎毫無信心。他們在報紙的專欄版上激烈爭論，似乎在最基本的問題上都無法達成共識。那么我們信任經濟學是不是在犯錯誤？經濟學家是不是就是冒充內行的騙子，應該像中世紀怪人那樣遭到蔑視？還是說盡管他們有缺點，但他們真的是我們擁有的最好的專家？我沒有一個確定的答案，就像御醫的問題也沒有令人滿意的答案一樣。但是攻讀完經濟學博士學位后，我的確知道一些我認為公眾對這個領域應該了解的事情。

首先，我們需要簡單談談經濟理論學家是做什么的?；旧希麄兪窃诮⒛Ｐ停Ｐ捅徽J為是用來描述經濟如何運行的數學工具。問題是經濟學家還未真正地創建出一個有效的整體經濟模型。很多聰明人士已經花費了大量時間創造出了名稱諸如“動態隨機一般均衡”的工具。但截至目前，這些模型無法像我們的氣象學家預測天氣那樣真正地預測經濟。而且這些模型包含著很多明顯錯誤的假設。就舉一個例子吧，很多模型規定，只允許公司不定時地調價！很荒唐，是吧？經濟學家納入這樣的假設是為了使模型更容易使用，而且他們希望這些可笑的假設其實相當接近于世界真正的運行方式。但是即便這些勉強拼湊的內容成立，在預測經濟方面，現有模型中也沒有哪個能發揮多大作用。

理論不是唯一的問題。經濟學家其實也沒有足夠好的數據來理解經濟是如何運作的。對于化學或者生物學，你可以把東西放到實驗室中，并利用可控實驗對它們進行測試。對于研究具體市場的微觀經濟學，你可以做類似的事情。但是對于將經濟作為整體來研究的宏觀經濟學，你無法把國家和整個經濟體放進實驗室，你能做的就只是坐看歷史變遷并試圖推斷出某些經濟模式。但往往就在你認為自己找到了某種模式時，它們就消失了。

正如宏觀經濟學缺乏生物學和化學那樣的數據標準一樣，它也缺乏這兩個領域所享有的那種科學文化。在硬科學中，模型為了解釋數據而建，這就是它們唯一的目的。但在經濟學中，模型往往只被當成講故事的工具，用來解釋關于世界可能會如何運作的某種觀點。

頂級的經濟學家們十分清楚自己的無知。（美國）聯邦儲備局主席本·伯南克最近在普林斯頓大學發表了畢業演講，期間他對聽眾半開玩笑說：“經濟學是一個高度復雜的思想領域，非常擅長向決策者們清晰準確地解釋他們過去的選擇為什么是錯誤的，但對于未來，就不那么擅長了?！笔澜缟献钪暮暧^經濟學家之一格雷格·曼昆在2011年《紐約時報》的專欄中如此表述了這樣的感想：

“在當了超過25年的職業經濟學家后，我有件事要坦白：對于經濟，我有很多不了解的地方。事實上，研究經濟周期起伏的經濟學領域是我投入精力最多、關注最多的領域，卻也是我發現自己最常遇到一些沒有明顯答案的重要問題的領域……”

所有這些都意味著，當一位經濟學家告訴你基于某種理論或某個模型推導出的事情時，你應當對此持強烈的懷疑態度。而且該理論或模型越復雜，你就越應該感到可疑。對使用花哨模型的經濟學家要多留神。

如果經濟學家確實成功創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“美聯儲應當印更多的錢嗎？”）并完全信任他們的專家建議。但在那一天到來之前，所有經濟學家真正能給我們的是直覺、建議和想法。就像那位皇家御醫一樣，我們每個人接下來都不得不自己確定，什么才是我們認為最好的藥物。因而當你聽經濟學家講話時，關鍵是嘗試去理解他們為什么會產生那種想法。例如，保羅·克魯格曼認為，在經濟蕭條期，貨幣政策的效果并不好，因為名義利率不能降到零以下，而且因為美聯儲并不總是擅長說服人們相信美聯儲將在未來允許通貨膨脹。羅伯特·巴羅認為財政政策沒有效果，因為人們預計今天的刺激政策需要未來的稅收來買單，于是減少當前的消費以儲備資金，用于支付這些未來的稅賦。大多數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，哪些看法他們認為是不現實的。

經濟學家還有另一個美德，就是他們非常善于指出彼此的邏輯錯誤。總體而言，經濟學家們都是非常聰明、敏銳的人。就像其他所有人那樣，他們容易過分自信并過于依賴自己未經證實的理論。但是當他們這么做時，其他經濟學家通常會逮他們個正著！因此，為了避免過分相信某位經濟學家聽上去自信的臆斷，你應當聽聽在此問題上持另一種意見的經濟學家有何觀點。

經濟學家并不是知道世界如何運轉或該如何對其進行精細調整的關鍵專家，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，你應當立即產生懷疑。但是他們的確有很多有趣的意見可以提供。他們可能會幫助你澄清或重新評估你自己關于經濟如何運轉的看法。他們還能夠幫助你發現別人論斷中的缺陷。

最終，你是那位皇家御醫。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. （中世紀生理學中所稱對人的健康和性情起決定作用的）體液

3. epistle [??p?sl] n. 書信體詩文

4. bread mold：[微]面包霉（通常指出現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）

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

9. crank [kr??k] n. 怪人

10. for all：雖然，盡管

11. dynamic stochastic general equilibrium：動態隨機一般均衡，該模型是目前貨幣政策分析與經濟預測的重要工具。

12. meteorologist [?mi?ti??r?l?d??st] n. 氣象學家

13. stipulate [?st?pjule?t] vt. 規定

14. zany [?ze?ni] adj. 滑稽的；愚蠢的

15. kludge [klu?d?] n. 為某個目的而勉強拼湊的內容

16. caliber [?k?l?b?（r）] n. 水準，質量

17. hard science：硬科學，自然科學與技術科學兩大系統所有學科與其交叉學科的統稱，借用電子計算機的“硬件”而得名。研究領域包括數學、物理學、化學、天文學、地理學、生物科學以及技術工程等學科。

18. Ben Bernanke：本·伯南克（1953～），美國經濟學家，現任美國聯邦儲備局（簡稱“美聯儲”）主席。

19. Greg Mankiw：格雷格·曼昆（1958～），美國著名經濟學家，29歲成為哈佛大學歷史上最年輕的終身教授之一，2003年走入政壇，著有《經濟學原理》、《宏觀經濟學》等經典教材。

20. Paul Krugman：保羅·克魯格曼（1953～），美國經濟學家，自由經濟學派的新生代，理論研究領域是貿易模式和區域經濟活動，2008年獲諾貝爾經濟學獎。

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

22. Robert Barro：羅伯特·巴羅（1944～），當今世界最具影響力的經濟學家之一，凱恩斯經濟學的代表人物，由于他在宏觀經濟學、經濟增長、貨幣理論與政策等領域所做出的卓越貢獻，被推選為美國藝術與科學學院院士。

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

24. go-to：關鍵的，靈魂的