The stock market jumped 6% last week on growing hopes of an imminent economic recovery. It has risen 39% from the March lows on similar hopes. Of course, it had previously fallen nearly 60% on fears of a slump.

All these moves have one thing in common: Millions of investors have acted on the belief that share values are closely related to what will happen in the economy in the next few months and years. But are they right?

Not according to Ben Inker, director of asset allocation at contrarian fund company Grantham Mayo Van Otterloo & Co. In a recent and fascinating note ('Valuing Equities in an Economic Crisis, or How I Learned to Stop Worrying about the Economy and Love the Stock Market'), Mr. Inker persuasively argues that the next moves in the economy shouldn't actually matter too much to investors at all.

Why? Two reasons.

First, because most of the value of shares really depends on the cash they will generate many years, even decades, ahead. The next few years are only a minuscule part of the equation. 'Since stocks do not have an expiration date and dividends grow over time,' Mr. Inker argues, 'the duration of stocks is extremely long. If we assume that half of the return from stocks in a given year comes from the dividends and half from the growth in dividends, most of the value of stocks comes from cash flows in the distant future.'

How distant? Using Mr. Inker's hypothesis, it turns out that about 75% of the value of shares is actually based on dividends that will be paid more than eleven years from now. Half the value is based on dividends to be paid after 25 years, and a quarter on those to be paid after about 50 years.

In other words, when you look at the market today, three quarters of its true value is based on what companies will earn and pay out after 2020 and half is based on what they will do after 2034. So really, how much attention should you pay to next quarter's earnings?

This is counterintuitive to most investors. Mr. Inker does not go into his math in detail, but some simple calculations may illustrate the point. Imagine, in a perfect world of smooth returns, you buy a $100 basket of shares today with a 7% earnings yield. They pay out half these annual earnings in dividends, and reinvest the rest to grow. In the first year you have a $100 investment earning $7 and paying $3.50 in dividends. In year two that's grown to a $103.50 investment earning $7.25 and paying about $3.62 in dividends. And so it goes over time. After 10 years your investment has grown to $141 and the dividends are $4.94. By year 25 the investment is worth $236, and the dividends are $8.27. If you look out 100 years, your investment is worth a remarkable $3,119 and the dividends are $109, or more than the original purchase price.

You probably won't hold on till then. (Your grandchildren might not, either.) But the value of that soaring income stream is built into the price we pay when we buy shares today for $100, and sell them 25 years from now for $236. Even after discounting future earnings -- a dollar next year is worth slightly less than this year, and so on -- these distant earnings form an incredibly large part of today's value, simply because they are so large.

There is a second reason for not paying too much attention to the economy's next move. No matter what happens next month or next year, sooner or later the economy will probably find its way back onto its long-term path anyway. If we now boom wildly, we'll pay for it with weaker growth down the line. And if things are bad for a while, eventually they'll pick up. That can be true even for devastating blows. GMO's calculations show that by the late 1940s, Mr. Inker writes, the U.S. economy had returned to the long-term growth path 'as if the Depression had never happened.' And that was even true by the late 1950s for West Germany after the devastation of the Second World War.

This sort of analysis is a useful antidote to stock market moods.

Wall Street is back on its happy pills again. At some point, maybe even soon, brokers may start urging us to pay too much for stocks on the basis of this year's economic growth or next. Canny investors may respond: But what about 2034?

对经济复苏指日可待的希望日益加大，受此提振，美国股市上周涨了6%。在同样希望的推动下，股市较3月份的低点涨了39%。当然，受经济滑坡担忧的拖累，美股此前跌了近60%。

股市的所有这些走势都有一个共同点，那就是数百万投资者的行为都是基于这样一种观点：股价与未来几个月和未来几年的经济形势密切相关。不过他们的看法对吗？

反向投资基金公司Grantham Mayo Van Otterloo & Co.的资产配置主管本•印克(Ben Inker)可不这样认为。在最近一份颇有趣的报告中，印克很有说服力地辩称，投资者实际上不应该过于看重近期的经济走势。

为什么？原因有二。

首先是因为股票价值大部分取决于未来很多年甚至几十年里股票产生的现金。今后的几年只是其中很短的一段时间。印克说，由于股票没有到期日，股息随着时间的增长而增长，股票持续非常长的时间。如果我们假定某一年里股票的一半收益来自股息，另一半来自股息的增长，那么大部分股票价值都来自遥远未来的现金流。

多远的未来？利用印克的假设得出，约75%的股票价值实际上取决于未来11年之后的股息收入。一半的股票价值取决于25年之后的股息，四分之一的股票价值取决于50年之后的股息收入。

也就是说，当你看今天的股市时，真正价值中的四分之三要看2020年之后公司的盈利和股息，一半的价值要取决于公司2034年之后的表现。因此，你该对下个季度的公司收益投入多大的关注呢？

大部分投资者的直觉看法都不是这样。印克没有详细介绍他的算法，不过一些简单的计算可能会阐明这点。想像一下，在回报平稳的完美世界中，今天你花100美元买了一篮子股票，收益率为7%。他们把年度收益的一半用来支付股息，另一半用于再投资发展业务。第一年，你的100美元投资可以盈利7美元，支付的股息为3.50美元。第二年，你的投资就成了103.50美元，可以盈利7.25美元，股息为3.62美元。如此下去......十年之后，你的投资就增长到了141美元，股息为4.94美元。二十五年后，你的投资为236美元，股息为8.27美元。一百年后，你的投资价值为惊人的3,119美元，股息为109美元，也就是比最初买进股票的价格还要高。

你或许坚持不到那个时候。（你的孙子可能都坚持不到。）不过这股不断飙升的收入流的价值会在我们今天以100美元的价格买进、25年后以236美元卖出时得到体现。即便是把未来收益打个折扣──明年1美元的价值略低于今年，等等──仅仅因为这些遥远未来的收益非常之大，它们就会构成今天价值的相当大一部分。

不要对短期的经济走势关注过多，这还有一个原因。无论下个月或是明年发生什么事，经济或许早晚都会重新回到长期的发展道路上去。如果现在经济疯狂增长，那么代价就是今后增幅会减小。如果一段时期形势不好，最终总会好起来的。即使是对灾难性的打击也是这样。印克写道，据Grantham Mayo Van Otterloo & Co.计算，到上世纪40年代末，美国经济已经回到了长期的增长道路上，就像大萧条从来没有发生过一样。对50年代末经历了二战的毁灭性打击之后的西德来说更是如此。

这类分析是对股市情绪的一剂有效的"解毒剂"。

华尔街又开始吃"忘忧药"了。有一天，或许很快，经纪商就可能开始敦促我们根据今年或明年的经济增长情况花高价买股票了。谨慎的投资者可能会回应：2034年时的情形又会怎样呢？
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