你应该把所有积蓄都投入股票吗？

经济学人：

Less than two months of 2024 have passed, but the year has already been a pleasing one for stockmarket investors. The s&p 500 index of big American companies is up by 6%, and has passed 5,000 for the first time ever, driven by a surge in enthusiasm for tech giants, such as Meta and Nvidia. Japan’s Nikkei 225 is tantalisingly close to passing its own record, set in 1989. The roaring start to the year has revived an old debate: should investors go all in on equities?

2024年虽然过去了不到两个月，但对于股市投资者来说，这一年已经是令人欣喜的一年。在人们对 Meta 和 Nvidia 等科技巨头的热情高涨的推动下，美国大公司的标准普尔 500 指数上涨了 6%，首次突破 5,000 点。日本日经 225 指数非常接近于超越其 1989 年创下的纪录。今年开局的强劲表现再次引发了一场古老的争论：投资者是否应该全力投资股票？

A few bits of research are being discussed in financial circles. One was published in October by Aizhan Anarkulova, Scott Cederburg and Michael O’Doherty, a trio of academics. They make the case for a portfolio of 100% equities, an approach that flies in the face of longstanding mainstream advice, which suggests a mixture of stocks and bonds is best for most investors. A portfolio solely made up of stocks (albeit half American and half global) is likely to beat a diversified approach, the authors argue—a finding based on data going back to 1890.

金融界正在讨论一些研究成果。其中一篇由 Aizhan Anarkulova、Scott Cederburg 和 Michael O’Doherty 三人于 10 月出版。他们提出了 100% 股票投资组合的理由，这种方法与长期以来的主流建议背道而驰，主流建议认为股票和债券的混合对大多数投资者来说是最好的。作者认为，仅由股票组成的投资组合（尽管一半是美国股票，一半是全球股票）可能会击败多元化投资策略——这一发现基于可追溯至 1890 年的数据。

Why stop there? Although the idea might sound absurd, the notion of ordinary investors levering up to buy assets is considered normal in the housing market. Some advocate a similar approach in the stockmarket. Ian Ayres and Barry Nalebuff, both at Yale University, have previously noted that young people stand to gain the most from the long-run compounding effect of capital growth, but have the least to invest. Thus, the duo has argued, youngsters should borrow in order to buy stocks, before deleveraging and diversifying later on in life.

为什么停在那里？尽管这个想法听起来很荒谬，但普通投资者举债购买资产的想法在房地产市场被认为是正常的。一些人主张在股票市场采取类似的做法。耶鲁大学的伊恩·艾尔斯和巴里·内勒巴夫此前曾指出，年轻人将从资本增长的长期复合效应中获益最多，但可投资的却最少。因此，两人认为，年轻人应该借钱购买股票，然后在以后的生活中去杠杆化和多元化。

Leading the other side of the argument is Cliff Asness, founder of aqr Capital Management, a quantitative hedge fund. He agrees that a portfolio of stocks has a higher expected return than one of stocks and bonds. But he argues that it might not have a higher return based on risk taken. For investors able to use leverage, Mr Asness argues it is better to choose a portfolio with the best balance of risk and reward, and then to borrow to invest in more of it. He has previously argued that this strategy can achieve a higher return than a portfolio entirely made up entirely of equities, with the same volatility. Even for those who cannot easily borrow, a 100% equity allocation might not offer the best return based on how much risk investors want to take.

争论的另一方是定量对冲基金 aqr Capital Management 的创始人 Cliff Asness。他同意股票投资组合的预期回报率高于股票和债券投资组合的预期回报率。但他认为，根据所承担的风险，它可能不会获得更高的回报。阿斯内斯认为，对于能够使用杠杆的投资者来说，最好选择风险与回报最佳平衡的投资组合，然后借钱投资更多的投资组合。他此前曾表示，在波动性相同的情况下，这种策略比完全由股票组成的投资组合可以获得更高的回报。即使对于那些无法轻松借贷的人来说，根据投资者愿意承担的风险程度，100% 的股权配置也可能无法提供最佳回报。

The problem when deciding between a 60%, 100% or even 200% equity allocation is that the history of financial markets is too short. Arguments on both sides rely—either explicitly or otherwise—on a judgment about how stocks and other assets perform over the very long run. And most of the research which finds that stocks outperform other options refers to their track record since the late 19th century (as is the case in the work by Ms Anarkulova and Messrs Cederburg and O’Doherty) or even the early 20th century.

在决定 60%、100% 甚至 200% 股权配置时，问题在于金融市场的历史太短。双方的论点（无论是明确的还是其他的）都依赖于对股票和其他资产长期表现的判断。大多数发现股票表现优于其他期权的研究都指的是股票自 19 世纪末以来的业绩记录（正如 Anarkulova 女士、Cederburg 和 O’Doherty 先生的工作中的情况），甚至是 20 世纪初。

Although that may sound like a long time, it is an unsatisfyingly thin amount of data for a young investor thinking about how to invest for the rest of their working life, a period of perhaps half a century. To address this problem, most investigations use rolling periods that overlap with one another in order to create hundreds or thousands of data points. But because they overlap, the data are not statistically independent, reducing their value if employed for forecasts.

尽管这听起来似乎很长一段时间，但对于一个正在思考如何在余下的职业生涯（也许是半个世纪）中进行投资的年轻投资者来说，这些数据的量实在是少得令人不满意。为了解决这一问题，大多数研究都使用相互重叠的滚动周期来创建数百或数千个数据点。但由于它们重叠，这些数据在统计上并不独立，如果用于预测，它们的价值就会降低。

Moreover, when researchers take an even longer-term view, the picture can look different. Analysis published in November by Edward McQuarrie of Santa Clara University looks at data on stocks and bonds dating back to the late 18th century. It finds that stocks did not consistently outperform bonds between 1792 and 1941. Indeed, there were decades where bonds outperformed stocks.

此外，当研究人员采取更长远的眼光时，情况可能会有所不同。圣克拉拉大学的爱德华·麦夸里 (Edward McQuarrie) 在 11 月发表的分析研究了 18 世纪末的股票和债券数据。研究发现，1792 年至 1941 年间，股票的表现并不总是优于债券。事实上，有几十年债券的表现优于股票。

The notion of using data from such a distant era to inform investment decisions today might seem slightly ridiculous. After all, finance has changed immeasurably since 1941, not to mention since 1792. Yet by 2074 finance will almost certainly look wildly different to the recent era of rampant stockmarket outperformance. As well as measurable risk, investors must contend with unknowable uncertainty.

使用如此遥远时代的数据来为今天的投资决策提供信息的想法可能看起来有点荒谬。毕竟，自 1941 年以来，金融业已经发生了不可估量的变化，更不用说自 1792 年以来了。然而，到 2074 年，金融业几乎肯定会与近期股市表现强劲的时代截然不同。除了可衡量的风险外，投资者还必须应对不可知的不确定性。

Advocates for diversification find life difficult when stocks are in the middle of a rally, since a cautious approach can appear timid. However financial history—both the lack of recent evidence on relative returns and glimpses at what went on in earlier periods—provides plenty of reason for them to stand firm. At the very least, advocates for a 100% equity allocation cannot rely on appeals to what happens in the long run: it simply is not long enough. ■

当股市上涨时，多元化的倡导者会发现生活很困难，因为谨慎的做法可能会显得胆怯。然而，金融历史——缺乏近期相对回报的证据以及对早期发生的情况的一瞥——为他们提供了充分的理由坚持立场。至少，100%股权分配的倡导者不能依赖于长期发生的事情：它根本就不够长。