As they turn the calendar to September, investors have good reason to be wary. 日子前进到九月，投资者有适当警觉一起了。The docket is full of news that could disrupt the Standard Poors 500s roughly 7% climb since June. On Friday, the Labor Department releases the latest jobs figures. On Sept. 12, a German court rules on the constitutionality of a critical rescue fund for the euro zone. And the Federal Reserve is expected soon to make clear whether there will be a third round of quantitative easing. 从日程表上的最重要事件来看，标准普尔500指数自六月以来约7%的升幅随时有可能玩完。

8月31日，美国劳工部(Labor Department)发布了近期的低收入数据。9月12日，德国某法院将就欧元区一个关键的救助基金计划否合乎宪法规定做出判决。

此外，美联储(Federal Reserve)估算迅速也将就否发售第三轮“分析严格”政策做出具体表态。But of special interest to historians is the calendar itself. Put simply, Sept. 1 marks the start of a historically miserable month for stocks. 但在史学家的眼里，日程表本身最有意思。因为历史经验指出，一旦日历翻到9月1日，对美国股市来说就意味著凄惨的一个月开始了。That isnt reason enough for investors to make any drastic moves with their portfolios. But they could profit by avoiding stocks that have suffered pullbacks, say some analysts. 这当然足以促成投资者对自己的投资人组做出任何根本性调整。

但有分析师回应，投资者如果需要回避那些历年来习惯在九月暴跌的股票，就有可能利润。Since 1926, in any given month, stocks of large companies have risen 0.9% on average, according to Bank of America Merrill Lynch. But in September, they have fallen by 0.8%, the only month with a negative average return. 据美银美林(Bank of America Merrill Lynch)统计资料，自1926年以来的给定月份，大盘股平均值下跌0.9%，但唯有九月其平均值展现出是暴跌的，这个月大盘股平均值暴跌0.8%。

For whatever reason, theres a predictable pattern where September has bad performance, says Steven DeSanctis a strategist with Bank of America Merrill Lynchs equity research team. 美银美林股票研究团队的策略师史蒂文德森提斯(Steven DeSanctis)回应，不论出于何种原因，九月美股展现出劣早已有定式难以确定。The trend has baffled researchers for decades. Striking September events, such as the 2008 collapse of Lehman Bros. and the 2001 terrorist attacks, are partly responsible for the bad average, but they cant explain the problems entirely. 这种定式早已后遗症了研究人员数十年。一些“恰巧”再次发生在九月份的大事件，例如2008年的雷曼兄弟(Lehman Bros)破产、2001年的恐怖袭击，与股市在九月份差劲的平均值展现出不无关系，但即便如此，也无法原始地说明这个现象。

For example, stocks have risen in only 50% of Septembers since 1926, the worst of any month and far below the 61.8% average success rate. 例如，自1926年以来的所有九月中，只有50%的情况是股市下跌的，比其他任何月份的统计资料结果都要劣，近高于61.8%的平均值下跌几率。If someone started investing in 1802 and kept his money in stocks only during September, he would have lost more than half of his money by 2006, according to researchers at the University of Kansas. Do the same during any other month, and he would have gained at least 79% during the period. 堪萨斯大学(University of Kansas)的研究人员找到，如果某位投资者从1802年转入股市，而且只在九月展开投资，那么到2006年他不会亏掉一半以上的资金。而在某种程度的时间和条件下，如果换作其他任何一个月份，这位投资者的账面价值最少不会下跌79%。

Explanations for the September swoon are hard to come by, and harder to swallow. 美国股市的九月厄运让人很难木村，而且至今也没一个令人信服的说明。The University of Kansas study suggests a sharp drop-off in the amount of daylight in New York in September might trigger seasonal affective disorder and make some traders more risk-averse. On average, New Yorkers see 3,147 fewer minutes of daylight in September than they do in August, the biggest drop of any month, according to the study. 堪萨斯大学的研究推断，九月份纽约白昼时间的大幅度锐减有可能引起了季节性的情绪失调，造成一些交易员的挂钩情绪减轻。此项研究找到，在纽约，九月的白昼比八月平均值增加3147分钟，减幅为各月之最。

But even the researchers arent confident in that explanation. From the best of my ability, I think theres something up with September. No matter how you slice it up, its bad, says the University of Kansas Mark Haug, one of the authors of the report. Its frustrating to not have an explanation. 但即便研究人员自己对这个说明也不过于确认。该研究论文的公开信作者、堪萨斯大学的马克豪格(Mark Haug)说道，“我最多不能说道，九月份显然有些不同寻常的事再次发生。不管是什么，都很差劲。

但去找将近一个合理的说明让人很心碎。” To be sure, Septembers poor performance could be due to mere chance. I always look at this stuff and wonder, Is it randomness? says Sam Stovall, chief equity strategist with SP Capital IQ. 当然，九月股市展现出差劲也有可能几乎归属于无意间事件。标普资本智商公司(SP Capital IQ)首席股票策略师山姆斯托瓦尔(Sam Stovall)回应，“我不免想起这件事，就不禁纳闷，‘这不会会就是随机性的呢？’” Mr. Stovalls theory: poor earnings guidance for the third quarter and the rest of the calendar year causes weary investors to sell shares. 斯托瓦尔的说明是：公司佳的第三季度及当年先前时间盈利预测促成慎重的投资者抛股票。

Another possibility posed by researchers: tax-loss harvesting. A 1986 law forced most mutual funds to move the end of their tax years to October. So, many portfolio managers might be selling stocks with recent losses in September and October to take advantage of tax breaks, says Scott Gibson, a finance professor at the College of William and Mary who has studied the phenomenon. 研究人员明确提出的另一个庞加莱是：税收亏损收成(tax-loss harvesting)。根据1986年制订的一项法律，大多数联合基金的税收年度必需在10月份累计。威廉玛丽学院(College of William and Mary)的金融学教授斯科特吉布森(Scott Gibson)回应现象也展开了研究，他回应，因为这个规定，很多投资人组基金经理可能会在九月和十月变卖最近有浮动亏损的股票，以取得减免税的益处。In 1990, when the rules took full effect, stocks with recent losses that were widely held by mutual funds lagged their benchmarks by almost 7 percentage points in October. Those same stocks beat their benchmarks by nearly 7 points in November, as the effect wore off, Prof. Gibson says. 吉布森教授认为，1990年，上述法规几乎生效时，联合基金广泛持有人的最近浮亏的股票在十月份跑完赢对应的基准指数将近七个百分点。

而到了十一月，税收效应消失后，某种程度一拨股票又跑完输掉基准指数将近七个百分点。Since then, the effect has become less pronounced, presumably as more mutual funds caught on. 此后，税收效应的影响显得仍然那么显著，这也许是因为有更加多联合基金参予了进去。

But Prof. Gibson says it is strong enough that investors looking to pick up shares on the cheap would be well-served to wait. Companies that have more than 5% of their shares held by funds and have seen recent losses are candidates for continued drops in September and October, he says. 但吉布森教授回应，税收效应的影响还是相当大的，期望抄底的投资者应该冷静等候。他说道，基金股权比例多达5%且近期有浮亏的上市公司，其股价最有可能在九月和十月之后暴跌。That would disqualify computer-seller Dell, which has dropped 10.8% in the last three months and is about 32% owned by mutual funds. 电脑销售公司戴尔(Dell)或许很合乎这个标准，该股过去三个月暴跌了10.8%，其联合基金的股权比例高达32%左右。

Other companies with poor recent performance and high fund ownership include Delta, Ford, Hewlett-Packard,Netflix, and Research In Motion. 其他近期股价走弱且基金股权比例较高的上市公司还包括达美航空(Delta)、福特汽车(Ford)、惠普(Hewlett-Packard)、Netflix和Research In Motion等。But with rational explanations hard to come by, investors should stop short of making big moves out of equities, Mr. Stovall says. 但斯托瓦尔认为，对于美股的九月厄运，由于很难寻找合理的说明，投资者也不该乘机做空股票。Youre better off treating this information the way you would the pilot coming over the loudspeakers and saying Please fasten your safety belt, Mr. Stovall says. Hes not saying Don the parachutes and assemble by the door. 斯托瓦尔说道，对于这个九月效应和分析人士的警告，投资者最差就像在坐飞机时对待机长通过麦克风的大喊一样，“系由好安全带”就行了，而不该将机长的大喊解读为“背上降落伞包在，到机舱门口子集”。

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