If you are looking for an investment portfolio that you could just forget about -- and which would still earn good returns in any environment -- what would you put into it?如果你在找一个可以放任不管、但在任何环境下都仍会产生不错回报的投资组合，那么这个投资组合会由哪些东西组成呢？

It is surprisingly hard to find a good answer -- especially in the current situation, with stocks and bonds seeming so expensive.好答案特别难找——特别是在当前环境中，股票和债券显得如此昂贵的情况下。

Investment advisers and managers usually recommend some variant of 60% stocks and 40% bonds (with fewer stocks and more bonds as you get older). The portfolio should be rebalanced at least once a year -- selling some of what has done well to buy more of what has done poorly, restoring the target proportions.投资顾问和理财经理一般是推荐60%股票加40%债券之类的组合（随着年龄的增长，股票少一些，债券多一些）。这样一个投资组合一年至少要做一次“再平衡”——把某些表现好的卖掉，买进更多表现差的，从而恢复最初设定的比例。

The theory is that when stocks do badly bonds will do well, and vice versa. But the theory is flawed.其理论依据是，股票表现差的时候债券表现会很好，反之亦然。但这套理论是有缺陷的。

Historically, this portfolio has only succeeded when stocks, or bonds, or both, have been reasonably valued or cheap. In the past, if you had invested in this portfolio when stocks and bonds were both overvalued, it proved a very poor deal.从历史上看，上述投资组合只有在股票或债券或两者估值合理或价格便宜的时候才取得了成功。在过去，如果你在股票和债券双双估值过高的时候投入这个投资组合，事实证明它将是一桩非常不划算的买卖。

Using data on stock and bond returns from New York University's Stern School of Business and inflation data from the Labor Department, I looked at how such a portfolio performed in the past when measured in real, inflation-adjusted dollars.利用纽约大学(New York University)斯特恩商学院(Stern School of Business)的股票债券回报率数据和美国劳工部(Labor Department)的通胀数据，我考察了上述投资组合在过去经通胀因素调整的表现。

It lost a third of its value from 1928 to 1932, and it lost value over two longer periods as well, from 1936 to 1947 and from 1968 to 1982 -- even before deducting taxes and costs. In reality, most investors would have done very badly indeed.这个投资组合从1928年到1932年损失了三分之一的价值，在1936年到1947年、1968年到1982年这两个更长的时间段内同样贬值——这还没有扣除税款和费用。事实上在现实生活中，多数投资者这样投资都会损失惨重。

What about now?现在呢？

U.S. stocks today look ominously expensive by the same measures that flashed red in 1928, 1936 and 1968. The S&P 500, for example, now trades at 25 times the past decade's per-share earnings, according to data tracked by Yale University economics professor Robert Shiller. The historic average is 16 times.按照1928年、1936年和1968年发出警报信号的同一批指标衡量，今天的美股显得非常昂贵，透露着不祥的信息。比如，耶鲁大学(Yale University)经济学教授罗伯特·席勒(Robert Shiller)跟踪的数据显示，目前标准普尔500指数(S&P 500)的价格达到过去10年每股利润的25倍，而历史平均值是16倍。

Nonfinancial stocks now trade for one times the value of company assets, a measure known as the 'q,' according to Federal Reserve data. The historical average is about 0.6 times, according to London University finance professor Stephen Wright.Xinhua/Zuma Press美联储主席贝南克：继续“缩减”可能有害于债市。根据美联储(Federal Reserve)的数据，现在非金融股的价格是公司资产价值的一倍。这个指标被称为“q比率”。据伦敦大学(London University)金融学教授史蒂芬·莱特(Stephen Wright)研究，q比率的历史平均水平约为0.6倍。

Back-testing suggests that both of these measures have been powerful predictors of future stock returns since the 19th century. Bond yields, meanwhile, are near historic lows due to the 'quantitative easing' policies of the Federal Reserve.The 10-year Treasury note yields just 3%, and corporate bond yields are near their lowest levels since the early 1960s.事后检验显示，自从19世纪以来，两个指标都是预测未来股市回报的强大工具。与此同时，债券收益率因为美联储的“量化宽松”政策处在接近历史最低的水平。10年期美国国债收益率仅3%，公司债券收益率接近20世纪60年代初期以来的最低水平。

Yes, inflation seems benign. But it always does when bond yields are low. Bond investors get hit by unexpected rises in inflation. Further Fed 'tapering' of its bond-market interventions, which begins next month, also could hurt bonds.没错，通胀现在显得很温和，但债券收益率低的时候通胀总是显得很温和。债券投资者会因为通胀率突然上升而受打击。美联储从1月份开始“缩减”对债券市场的干预，也有可能给债市造成伤害。

Based on the best estimates of GMO, a Boston money-management firm with $112 billion in assets, such a balanced portfolio of 60% stocks and 40% bonds is likely to earn meager returns over the next seven years or so.根据波士顿资产管理公司GMO（管理资产1,120亿美元）的估计，60%股票加40%债券的均衡投资组合在未来七年左右最多也只能获得微薄的回报。

What are your alternatives?还有哪些选择？

Market historian Rob Arnott, chairman of money-management and advisory firm Research Affiliates in Newport Beach, Calif., says that the ultimate 'universal' passive portfolio -- one designed to weather all environments -- would be equal parts real estate, commodities, stocks and bonds, rebalanced periodically to restore the initial proportions. His suggestion was inspired by the investments of Jakob Fugger, the German Renaissance financier.市场史学家、加州纽波特比奇(Newport Beach)资产管理与顾问公司Research Affiliates董事长罗布·阿诺特(Rob Arnott)说，旨在经受各种环境的终极“普世”被动型投资组合，将是房地产、大宗商品、股票和债券各占相同比例，并定期做“再平衡”恢复到原来的比例。他的这一建议是受到了德国文艺复兴时期金融家雅各布·富格尔(Jakob Fugger)所做投资的启发。

He adds that investors should buy global investments -- including emerging-market stocks and bonds -- and not merely those of the U.S.他补充说，投资者应当买进包括新兴市场股票和债券在内的全球性投资产品，而不只是美国的投资产品。

Alex Shahidi, a financial adviser at Bank of America Merrill Lynch in Los Angeles, argues for equal proportions of stocks, commodities, long-term government bonds and inflation-protected government bonds.美银美林(Bank of America Merrill Lynch)驻洛杉矶理财顾问亚历克斯·沙希迪(Alex Shahidi)主张均等配置股票、大宗商品、长期国债和通胀保值国债。

Commodities and real estate might do well in times of unanticipated inflation, offsetting any losses on bonds (and stocks).大宗商品和房地产在通货膨胀突然爆发的时候可能会有不错的表现，从而在债券（和股票）发生亏损的情况下给予补偿。

Others say investors should own natural-resources stocks instead of commodities, because of the transaction costs involved in funds that use commodity futures. Still others say investors include gold.另一些人说，投资者应当持有自然资源类股票而不是大宗商品，因为包含大宗商品期货的基金会涉及一些交易费用。还有一些人说，投资者应当把黄金包括进去。

All these suggestions depend on hypotheses. There simply aren't enough data for multiple asset classes over long periods to be certain. (Inflation-protected U.S. bonds, for example, didn't exist before the 1990s.) And existing data might not be that useful. Some markets, such as gold, have been changed fundamentally by the influx of retail investors.所有这些建议都是以假设为基础。要想有确切的依据，根本就没有足够的数据来呈现多种资产类别在长时间范围内的表现。（比如美国通胀保值国债在90年代以前是不存在的。）而且现有数据可能也没有多大用处。有些市场（比如黄金）已经因为散户的涌入而发生了根本性的变化。

Andrew Smithers, a financial consultant in London, looked at passive portfolios in detail a few years ago on behalf of the endowment committee of a college at Cambridge University in England. He argues for a simple portfolio of stocks and cash (such as short-term deposits), rebalanced annually. Cash is a better counterweight than bonds, he found, because it was less correlated to stocks -- and less vulnerable to inflation.伦敦理财顾问安德鲁·史密瑟斯(Andrew Smithers)在几年前为英国剑桥大学(Cambridge University)一个学院的捐赠基金委员会详细考察了被动型投资组合。他主张将投资组合简单地配置为股票和现金（比如短期存款），一年做一次再平衡。他发现现金的平衡作用强于债券，因为它与股票的关联度更低，并且受通货膨胀影响的程度也低于债券。

Mr. Smithers says the best long-term performance came from varying the proportion of stocks in the portfolio from year to year, between 60% and 100%. The ratio depends on how expensive stocks are based on long-term measures such as Mr. Shiller's 10-year price/earnings ratio or the 'q' ratio.史密瑟斯说，最好的长期表现来自每年将股票占投资组合的比例在60%到100%范围内进行调整，具体比例取决于股价按照长期指标（如席勒的10年往绩市盈率或“q比率”）衡量有多昂贵。

No past research can ever be an infallible guide to the future. Mr. Smithers's analysis offers the merits of simplicity and common sense.用对过去的研究来指导未来，绝对不可能完全可靠。史密瑟斯的分析具有简单、符合常理的优点。

Reason suggests two potential changes. The first is to invest in a global portfolio of stocks rather than merely in the U.S. The second is to include inflation-protected Treasury bonds, or TIPS, as well as cash in the nonstock portion, although Mr. Smithers demurs.按道理，可能要做两个方面的调整。第一个调整是投资于某个全球化的股票组合，而不只是投资美股。第二个调整是非股票部分除了现金以外，还要把通胀保值国债包括进去。不过史密瑟斯对此持有异议。

Simplicity is a virtue. But finding the right simple answer isn't as easy as it might sound.

简单即是美。但怎样找到正确而简单的答案，并不像表面看来那么容易。