The Royal Swedish Academy of Sciences continues to astonish the public when awarding the Nobel Memorial Prize in Economics. In 2011 it celebrated the success of recent research in promoting macroeconomic stability. This year it pays tribute to the capacity of economists to predict the long-run movement of asset prices.
       瑞典皇家科學院的諾貝爾經濟學獎頒獎結果又一次讓公眾跌破眼鏡。2011年，經濟學獎表彰的是近期研究在促進宏觀經濟穩定方面取得的成功；今年，則表彰了經濟學家對資產價格長期動向的預測能力。

       People with knowledge of financial economics may be further surprised that this year Eugene Fama and Robert Shiller are both recipients . Prof Fama made his name by developing the efficient market hypothesis, long the cornerstone of finance theory. Prof Shiller is the most prominent critic of that hypothesis. It is like awarding the physics prize jointly to Ptolemy for his theory that the Earth is the centre of the universe, and to Copernicus for showing it is not.
       瞭解金融經濟學的人士可能會對頒獎結果更感意外：今年的獲獎者既有 Eugene Fama ，又有 Robert Shiller 。 Fama 教授的成名作是提出了有效市場假說，它長期以來一直是金融理論的基石。 Shiller 教授則是該假說的最重要批評者。這好比把物理學獎同時頒給認為地球是宇宙中心的托勒密，以及證偽此學說的哥白尼。

       Actually, it is not as bad as that analogy suggests. Although the efficient market hypothesis is not true, the basic idea – that there is a tendency for publicly available information to be reflected in market prices – is an essential tool for anyone involved in securities markets. And while the claim that economists are good at predicting long-run asset prices is a stretch, Prof Shiller’s research supports strong evidence of long-run mean reversion, as prices return to the fundamental values established by the earning capacity of the underlying assets.
       事實上，情況並沒有上述類比中所暗示的那麼糟。儘管有效市場假說不符合事實，但其基本思想——即公開可獲得的資訊往往反映在市場價格中——是一切證券市場參與者的基本工具之一。另一方面，儘管關於經濟學家善於預測長期資產價格的斷言有些勉強，但 Shiller 的研究強有力地證明了長期“均值回歸”，即價格終將回歸到由基礎資產盈利能力確立的基本價值。

       Still, both these insights were available to market practitioners from common sense and casual observation long before the complex mathematics and extended data sets of academic financial economics. The prize committee gives the misleading impression that there is an agreed, established and advancing body of knowledge in financial economics: but the subject, for half a century a showpiece in economic departments and business schools because of its mix of intellectual rigour and practical relevance, is today struggling to maintain credibility in the face of the financial instability of the past two decades.
       不過，早在複雜的數學和金融經濟學龐大的資料集誕生之前，市場從業者便已經能從常識和平時的觀察中得出這兩項結論。諾獎委員會誤導人們認為，金融經濟學領域存在著一個公認的、成熟的、不斷發展的知識體系；但在半個世紀的時間裡因兼具學術嚴謹性和現實適切性而在經濟學系及商學院佔據重要地位的金融經濟學，卻在過去20年金融動盪的考驗下難以維繫其可信度。

       The problem is not the efficient market hypothesis itself, which should be understood as a tendency, not a law. The problem is with the superstructure built around it – a world of rational agents holding rational expectations achieving a state of “equilibrium” – a term economists have borrowed from physics – through trade with other rational agents holding similar rational expectations. In a masterpiece of persuasive language, the word “rational” is used to describe agents and expectations with a meaning very different from its ordinary usage.
       問題不在於有效市場假說本身（它應被理解為一種趨勢，而非定律），而在於圍繞它建立的上層建築——一群懷有理性預期的理性人通過與其他懷有類似理性預期的理性人進行交易，達到一種“均衡”態（“均衡”一詞系經濟學家借用自物理學）。在經典的說服性語言中，“理性”一詞用來描述個體和預期，其含義與該詞的一般用法截然不同。

       This theory is easier to defend for its logical consistency than for the supporting empirical evidence. The capital asset pricing model to which it gives rise offers a striking, and counterintuitive, proposition: that the idiosyncratic risk associated with individual speculative projects, such as pharmaceutical research or weapons programmes, needs no reward above that accruing to riskless investments; but the risk associated with macroeconomic uncertainty experienced by all companies will require a substantial premium. The most striking empirical demonstration that this prediction is not true is found in the work Prof Fama undertook himself; while the most important contribution of his co-laureate, Prof Shiller, was to show the volatility of stock market prices far exceeds that justified by new information relevant to fundamental values.
       比起實證證據，我們更容易從邏輯一致性的角度來為這個理論辯護。它引出的資本資產定價模型(CAPM)給出了一個很有意思且有悖直覺的主張：與個別投機項目（如藥品研究或武器項目）相關的獨特風險，並不要求獲得比無風險投資之回報更高的回報；但所有公司都會經歷的、與宏觀經濟不確定性有關的風險，卻要求很高的溢價。在實證上證偽這一預言的最顯著成果，恰恰來自法馬教授本人的研究；而同為獲獎者的席勒教授所做出的最重要貢獻，是證明股價波動性遠高於與基本價值有關的新資訊所應帶來的波動性。

       But we do not have to believe, like Prof Fama, that we all correspond to his concept of rationality or, like Prof Shiller, that we are slaves to our psychological weaknesses. There is a middle course, which understands that the economists’ use of the term “rationality” lacks relevance in a world characterised by imperfect information; that rational expectations are impossible in the face of radical uncertainty; and that it is implausible that constantly changing securities prices represent an equilibrium.
       不過，我們不必像法馬教授那樣認為我們所有人都符合他的“理性”概念，也不必像席勒教授那樣認為我們是自身心理弱點的奴隸。我們應當走一條中間道路，理解在一個以不完備資訊為特點的世界裡，經濟學家對“理性”一詞的使用缺乏適切性；理解在面對根本不確定性的情況下，理性預期是無從實現的；理解不斷變化的證券價格代表均衡態的觀點是站不住腳的。

       There was no scope for compromise on the nature of the physical world: Copernicus was right and Ptolemy was wrong. There are not, and will not be, equivalent certainties in economics, and if such certainty is the hallmark of science – I do not think it is – then economics is not a science. The resulting insecurity seems to lead the Nobel committee to claim more for the subject of economics than it has achieved.
       在物理學領域，對現象本質的理解曾不容折中：哥白尼就是對的，托勒密就是錯的。在經濟學領域，沒有也不會有與之相同的確定性。如果這種確定性是科學的特點——我並不這樣認為——那麼經濟學便不是一門科學。由此產生的不安感，似乎促使諾獎委員會誇大了經濟學這門學科所取得的成就。