永遠的泡沫

作者:13年諾貝爾經濟學獎得主 羅伯特·席勒  日期:2013-10-17 0:22:22  閱讀數:  網友評論:

(核心提示)

投機泡沫的最準確定義:關于價格上漲的新聞刺激了投資者熱情,投資者熱情通過心理感染傳播,并在此過程中放大可以證明價格上漲合理性的故事。”這吸引了“越來越龐大的投資者群體,他們盡管懷疑投資的真實價值,但也被吸引入局,部分是因為他們嫉妒他人的成功,部分是因為賭徒的興奮。”

羅伯特·席勒是2013年諾貝爾經濟學獎得主。作為新凱恩斯學派成員之一,席勒認為,市場并非總是有效的,投資者的情緒甚至外在氣候等因素都能對投資行為產生影響。

席勒同時也是一位暢銷書作者,《動物精神》和《非理性繁榮》使他的理論深入人心。

席勒與中國關系密切,曾多次到訪中國,并多次提及對中國房地產的看法,稱中國房地產泡沫嚴重。本欄目選登席勒的文章《永遠的泡沫》,供對看懂中國房市泡沫有著強烈的現實意義。

在2006年史上最大全球房地產泡沫破滅、2007年世界股市大泡沫結束之后,你大概以為我們已經進入了后泡沫時代。但關于泡沫的討論仍沒有淡出視野——許多國家的房地產市場仍有泡沫或出現了新的泡沫;新的全球股市泡沫;美國和其他國家長期債券市場泡沫;石油價格泡沫;黃金泡沫,等等。

盡管如此,當我上個月訪問哥倫比亞時,并沒有預期會看到泡沫。但是,人們再一次和我談到了進行中的房地產泡沫,我的司機指向海濱度假小鎮卡塔赫納(Cartagena),帶著驚愕的口氣說,有的房子最近賣到了數百萬美元。

哥倫比亞央行有一個追蹤三大城市——波哥大、麥德林和卡利的住房價格指數。自2004年以來,該指數實際值(經通脹調整)上漲了69%,其中大部分漲幅發生在2007年之后。房價上升之快令人想起了美國,標普/凱斯-希勒(S&P/Case-Shiller)十城市住房價格指數從1997年的底部到2006年的頂部總共上漲了131%。

問題由此而生:什么才是壯觀的泡沫?《牛津英語詞典》對泡沫的定義是“任何易碎、虛幻、空洞、無價值的東西;騙人的把戲。自17世紀以來常用于欺騙性的商業或金融計劃。”問題在于,“把戲”和“項目”之類的詞表明泡沫是有意為之之物,而不是不聽從任何人指揮的普遍的社會現象。

也許“泡沫”一詞有濫用之嫌。

尤金·法馬(Eugene Fama)顯然這樣認為。作為“有效市場假說”最重要的支持者,法馬否認泡沫的存在。在2010年接受《紐約客》采訪時,法馬對約翰·卡西迪(John Cassidy)說:“我甚至不知道泡沫是什么意思。這些詞倒是很流行。我不認為它們有什么意義。”

在我的書《非理性繁榮》(Irrational Exuberance)第二版中,我嘗試給泡沫下一個更好的定義。“投機泡沫”我寫道,是“這樣一種情況:

關于價格上漲的新聞刺激了投資者熱情,投資者熱情通過心理感染傳播,并在此過程中放大可以證明價格上漲合理性的故事。”這吸引了“越來越龐大的投資者群體,他們盡管懷疑投資的真實價值,但也被吸引入局,部分是因為他們嫉妒他人的成功,部分是因為賭徒的興奮。”

這似乎是泡沫這個詞最核心的意思,也是最常用的用法。這個定義隱含的含義是“聰明錢”為何極難通過賭反向下注從泡沫中賺錢:心理傳染催生了論證價格上漲合理性的觀念,因此參與泡沫可謂“幾乎”(almost)理性。但其實是不理性的。

每個國家的故事各不相同,因為各國各有各的新聞,與其他國家并不總是相同。比如,目前哥倫比亞的故事是,在總統桑托斯廣受好評的治理下,哥倫比亞政府將通脹和利率壓到了發達國家水平,此外,消除FARC叛軍的威脅不啻向哥倫比亞經濟注入了新活力。這個好故事足以推動住房泡沫。

因為泡沫從本質上說是一種社會心理學現象,因此天生難以控制。自金融危機以來的監管行動或許能抑制未來泡沫。但公眾對泡沫的恐慌也可能加強心理傳染,助長更加自我實現的預言。

泡沫一詞的一個問題是它創造了一幅擴張的肥皂泡心理情景,這個肥皂泡注定會突然地、不可逆轉地破滅。但投機泡沫并沒有那么容易結束;事實上,它們可能先因為故事的改變而收縮一定幅度,然后再度膨脹。

更準確的做法是將這些發作稱為投機傳染病。從流感中我們知道,新的傳染病可以在舊傳染病正在消失時突然爆發,如果新的病毒種類出現的話,或者如果某些環境因素提高了傳染率的話。類似地,一個新的投機泡沫可以隨時出現,如果關于經濟的新故事出現,且故事性足夠強以至于投資者被新思維傳染的話。

20世紀20年代美國牛市便是如此。這次牛市在1929年見頂。我們認為泡沫是一段價格狂飆突進的時期,接著是突如其來的轉折點和決定性的大跌,這扭曲了歷史。事實上,“黑色星期二”后,美國股市實際價格出現過一次大漲,1930年,股市收復了1929年跌幅的一半。接著到來的是第二次崩潰、1932—1937年的再次繁榮,以及第三次崩潰。

投機泡沫不會像短篇故事、小說或戲劇那樣結束。不存在將所有線索同時推向令人難忘的結局的劇終場景。在真實世界中,我們永遠不知道故事什么時候結束。

 

英文原題:Bubbles Forever

You might think that we have been living in a post-bubble world since the collapse in 2006 of the biggest-ever worldwide real-estate bubble and the end of a major worldwide stock-market bubble the following year. But talk of bubbles keeps reappearing – new or continuing housing bubbles in many countries, a new global stock-market bubble, a long-term bond-market bubble in the United States and other countries, an oil-price bubble, a gold bubble, and so on.

Nevertheless, I was not expecting a bubble story when I visited Colombia last month. But, once again, people there told me about an ongoing real-estate bubble, and my driver showed me around the seaside resort town of Cartagena, pointing out, with a tone of amazement, several homes that had recently sold for millions of dollars.

The Banco de la República, Colombia’s central bank, maintains a home price index for three main cities – Bogotá, Medellín, and Cali. The index has risen 69% in real (inflation-adjusted) terms since 2004, with most of the increase coming after 2007. That rate of price growth recalls the US experience, with the S&P/Case-Shiller Ten-City Home Price Index for the US rising 131% in real terms from its bottom in 1997 to its peak in 2006.

This raises the question: just what is a speculative bubble? The Oxford English Dictionary defines a bubble as “anything fragile, unsubstantial, empty, or worthless; a deceptive show. From 17th c. onwards often applied to delusive commercial or financial schemes.” The problem is that words like “show” and “scheme” suggest a deliberate creation, rather than a widespread social phenomenon that is not directed by any impresario.

Maybe the word bubble is used too carelessly.

Eugene Fama certainly thinks so. Fama, the most important proponent of the “efficient markets hypothesis,” denies that bubbles exist. As he put it in a 2010 interview with John Cassidy for The New Yorker, “I don’t even know what a bubble means. These words have become popular. I don’t think they have any meaning.”

In the second edition of my book Irrational Exuberance, I tried to give a better definition of a bubble. A “speculative bubble,” I wrote then, is “a situation in which news of price increases spurs investor enthusiasm, which spreads by psychological contagion from person to person, in the process amplifying stories that might justify the price increase.” This attracts “a larger and larger class of investors, who, despite doubts about the real value of the investment, are drawn to it partly through envy of others’ successes and partly through a gambler’s excitement.”

That seems to be the core of the meaning of the word as it is most consistently used. Implicit in this definition is a suggestion about why it is so difficult for “smart money” to profit by betting against bubbles: the psychological contagion promotes a mindset that justifies the price increases, so that participation in the bubble might be called almost rational. But it is not rational.

The story in every country is different, reflecting its own news, which does not always jibe with news in other countries. For example, the current story in Colombia appears to be that the country’s government, now under the well-regarded management of President Juan Manuel Santos, has brought down inflation and interest rates to developed-country levels, while all but eliminating the threat posed by the FARC rebels, thereby injecting new vitality into the Colombian economy. That is a good enough story to drive a housing bubble.

Because bubbles are essentially social-psychological phenomena, they are, by their very nature, difficult to control. Regulatory action since the financial crisis might diminish bubbles in the future. But public fear of bubbles may also enhance psychological contagion, fueling even more self-fulfilling prophecies.

One problem with the word bubble is that it creates a mental picture of an expanding soap bubble, which is destined to pop suddenly and irrevocably. But speculative bubbles are not so easily ended; indeed, they may deflate somewhat, as the story changes, and then reflate.

It would seem more accurate to refer to these episodes as speculative epidemics. We know from influenza that a new epidemic can suddenly appear just as an older one is fading, if a new form of the virus appears, or if some environmental factor increases the contagion rate. Similarly, a new speculative bubble can appear anywhere if a new story about the economy appears, and if it has enough narrative strength to spark a new contagion of investor thinking.

This is what happened in the bull market of the 1920’s in the US, with the peak in 1929. We have distorted that history by thinking of bubbles as a period of dramatic price growth, followed by a sudden turning point and a major and definitive crash. In fact, a major boom in real stock prices in the US after “Black Tuesday” brought them halfway back to 1929 levels by 1930. This was followed by a second crash, another boom from 1932 to 1937, and a third crash.

Speculative bubbles do not end like a short story, novel, or play. There is no final denouement that brings all the strands of a narrative into an impressive final conclusion. In the real world, we never know when the story is over.

(Robert J. Shiller is Professor of Economics at Yale University, the co-creator of the Case-Shiller Index of US house prices, and the winner of the 2013 Nobel Prize in Economics.)


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