10月10日，道瓊斯工業(yè)平均指數(shù)的跌幅達到了800點。同日，標普500指數(shù)也下跌近5%。這是否預(yù)示著美國股市一個具有歷史意義的大牛市即將終結(jié)？

股市是周期性波動的，一個節(jié)點是否是由牛市轉(zhuǎn)向熊市的拐點，只有進入了熊市之后才知道。目前，在整個股市的增值部分中，有相當一部分由以蘋果公司為代表的科技股主導(dǎo)，光是蘋果一家的市值就超過了萬億美元。在大盤普遍下跌的背景下，一些人對科技股尤為精神緊張，加劇了短期的暴跌。另外，美聯(lián)儲加息和就業(yè)的緊縮也讓投資者信心不足。

根據(jù)一些權(quán)威定義，所謂“熊市”，是指標普500指數(shù)至少要比牛市的頂點下跌20%以上；同理，所謂“牛市”至少要比熊市的最低點上漲20%以上。很多股市觀察人士認為，美股的本輪牛市由2009年3月9日起，到2018年10月10日止，是二戰(zhàn)以來為期最長的一次，持續(xù)了3503天。到8月22日，它已經(jīng)打破了“史上最長牛市”的紀錄——此前的紀錄是從1990年10月到2000年3月。

從歷史上看，二戰(zhàn)結(jié)束后，幾乎所有的熊市都始于持續(xù)而顯著的下跌，而不是簡單的波動。當全球金融和政治局勢不穩(wěn)定時，美股的跌幅可能會達到5%甚至10%以上，但之后就會出現(xiàn)類似幅度的上升。而熊市則是從持續(xù)的均勻下降開始的。

因此，在接下來的幾周至幾個月里，需要關(guān)注的跡象并不是股市的波動性，而是要觀察任何一段四到八周的時間里，市場的平均下行趨勢。

比如在1973到1974年的股災(zāi)中，標普500指數(shù)于1972年12月達到峰值——也就是700點左右。此后至1973年10月，標普500指數(shù)平均每個月下降1或2個百分點，總體跌幅達15%。隨后突然暴跌，到1974年9月又跌了40%，此時已經(jīng)觸底。此后，標普500指數(shù)直到1987年才恢復(fù)到700點。

自1975年以來，按通脹調(diào)整后的股市市值已經(jīng)增長了很多，不過每次熊市也再沒出現(xiàn)過那么大的跌幅。而且熊市后的牛市會快速收復(fù)失地，并且超過熊市前的頂點。

牛市經(jīng)常會因為一個決定性的事件而結(jié)束。比如1956年，美聯(lián)儲啟動加息，同年又發(fā)生了蘇伊士危機和匈牙利革命等事件，導(dǎo)致了投資者紛紛撤資。1987年10月19日是美股歷史上著名的“黑色星期一”，這一天，美股單日跌幅超過20%，此前股市的強勢反彈在波斯灣危機和貿(mào)易赤字的夾擊下迅速化為泡影。

上一輪牛市是2002年10月到2007年10月，由于通脹以及大量次級貸和其他不良貸款的發(fā)酵，這一輪牛市的崩潰迅速引發(fā)了全球性的金融危機。

值得欣慰的是，和牛市相比，熊市總是短暫的。最近的一輪熊市始于2007年，只持續(xù)了兩年半左右。不過此后的牛市卻足足花了四年的時間，才追上了2007年的最高值。（財富中文網(wǎng)）

譯者：樸成奎?

The 800-point drop of the Dow Jones Industrial Average on Oct. 10 may be a blip, and so could the nearly 5% decline over five days in the S&P 500. But they are also possibly leading indicators of the end of a historic bull market, in which stock-market indexes continue upward quarter after quarter.

Markets are cyclical, and experts only agree after the fact on what predicted an oncoming bearish period (and even then, often not). And right now tech stocks—like the trillion-dollar Apple—have dominated a significant part of the rise in value of the market as a whole. Jitters about those companies have led to this short-term fall, too, while drops were felt throughout the market. Rising interest rates from the Fed and a tight employment market don’t reassure investors, either.

A bear market by many definitions requires a drop of at least 20% in the S&P 500 from a bull-market peak; likewise, a bear market starts counting at a 20% rise out of a deep trough. Many stock-market observers pin the start of the current bull market, the longest since World War II, at March 9, 2009. As of October 10, it’s lasted 3,503 days. On August 22, it exceeded the previous record length, which ran October 1990 to March 2000.

Historically, almost all bear markets since World War II have started with consistent and significant ongoing declines, rather than simple volatility. Drops of 5% to 10%, or even higher, can occur during global financial and political uncertainty, but they’re paired with similar rises. Bear markets start with consistent average drops.

So, signs to watch for in the upcoming weeks and months aren’t volatility, but an average tendency for the market to head downward across any four-to-eight week period.

In the 1973–74 stock market crash, for instance, the S&P 500 peaked around 700 in December 1972, and then dropped a percentage point or two almost every month through October 1973, a 15% decline overall. But then it plummeted, crashing another 40% by September 1974, when it bottomed out. The index didn’t reach 700 again until 1987.

Bear markets since 1975 have had far lower percentage drops at their bottom, even as markets have grown remarkably in inflation-adjusted dollars. The following bull upswings more quickly regain lost ground and then exceed pre-bear highs.

Bull markets tend to end because of a defining event. In 1956, the Fed raised interest rates, while international events like the Suez Crisis and the Hungarian Revolution caused investors to pull back. In 1987, stocks dropped more than 20 percent on a single day—Black Monday, Oct. 19—after a strong rally crashed into the Persian Gulf turmoil and trade deficits.

The previous bear market, from October 2002 to October 2007, collapsed in the face of the global financial crisis, precipitated by raising interest rates in the face of inflation that revealed the vast scale of subprime mortgages and other badly collateralized loans.

The good news? Bear markets are short compared to bull runs. The most recent, starting in 2007, lasted about 2 1/2 years, though it took another four for the bull market to exceed highs reached in 2007.