為什麼要冒險投資股市﹖

投資者在2006年末和2007年初大舉進入股市﹐但股市一週來的疲弱表現卻給了他們當頭一棒﹐道瓊斯工業股票平均價格指數週二更是暴跌了416點。是“入不逢時”嗎﹖沒人知道股市在未來一年將如何表現﹐如果股市週三出現某種程度的回調人們也不必大驚小怪。

但有一點是很清楚的﹕許多投資者在股市上陷得過深﹐由此而額外承擔的風險有可能傷及他們。

•要瞭解問題所在﹐不妨設想現在是2006年初﹐而你手頭剛好有30萬美元退休儲蓄。

你將這筆錢的70%投向了股市﹐30%投入債市。你設想自己股市投資的長期回報率將為8%﹐而債市投資的長期回報率則為5%。與此同時﹐你還打算把自己未來12個月的8萬美元薪水存起12%﹐也就是9,600美元。

如果一切如你所願﹐那麼到2006年年底時﹐你手頭的資金將達到33.1萬美元。但實際情況是﹐雖然你的債券投資去年只增值了4%﹐但你的股市投資卻增值了16%﹐所以年底時你手頭的資金超過了34.7萬美元。其結果是﹐你比預期多賺了1.6萬美元。

這時人們通常給你的建議是﹕將股市和債市投資調整回7比3的比例﹐我認為這是個很不錯的建議。如果你禁不住誘惑繼續使投資於股市的資金高於70%會怎樣﹖

在我看來﹐如果你不想在投資分配比例問題上再傷腦筋﹐你應該將投資股市的資金降到70%以下才對﹐而不是高於這一比例。不管怎么說﹐你的退休金積累速度已經超過了你的預期﹐這意味著你在積攢退休金方面已沒有必要承受太多風險。

投資顧問威廉•伯恩斯坦(William Bernstein)說﹐投資時不能只考慮回報﹐還要注意控制風險。如果你已經贏得了比賽﹐繼續玩下去還有什麼意義﹖

•我已經聽到了一片質疑之聲。如果股市的投資回報率通常高於債市﹐為什麼不把更多的錢投向股市呢﹖如果你執行退休金積攢計劃的進度超過了預期﹐為什麼不能少攢一點或提前退休呢﹖

這條路並非走不通。但多一些謹慎可能也並非壞事。事實上﹐股市回報並非憑空得來的。相反﹐沒有經濟的增長和企業利潤的相應提高就沒有股價的上揚。

誠然﹐短期而言股價漲幅有可能高於經濟增長率。這或許是因為投機性買盤導致股票的本益比節節攀升﹐或許是因為企業利潤的增長率一兩年內超過了經濟增長率。

但長期而言﹐股價漲幅終將反映經濟增長率。以往50年中﹐標準普爾500指數的年均漲幅為7.1%﹐恰好與在此期間美國國內生產總值年均7.1%的增幅一致。如果再加上股息﹐投資股市的總回報率是10.6%。但必須牢記的一點是﹕我們投資股市不可能年年都獲得豐厚回報﹐股市大漲一段時間以後必然要經歷一段低迷期。

•如果你要10年或15年以後才退休﹐那就不必對股市近期的表現太過擔憂﹐包括週二的大幅下挫。相反﹐你不必急著從股市撤回投資﹐大可繼續“貪婪”地尋求投資高回報。

但那些已經退休或接近退休年齡的人卻應該認真想一想﹐你究竟需要多少錢來安度晚年﹐如果近年來的股市投資已使你賺了個缽滿盆盈﹐還有必要再冒那麼大的投資風險嗎﹖

如果你已攢足了養老錢﹐即使為了投資組合的多樣化﹐也應該繼續把至少30%或35%的資金投向股市。為你的繼承人著想﹐你或許也應該多承擔一些投資風險。伯恩斯坦說﹐如果你手頭的錢已超出了維持退休生活所必須的數額﹐那麼你承擔投資風險就不是為自己﹐而是為你的遺產受益人了。

Why risk it?

Investors piled into stocks in late 2006 and early 2007, only to see the market weaken over the past week, including yesterday's 416-point dive by the Dow Jones Industrial Average. Bad timing? Nobody knows how the market will fare in the year ahead, and some sort of bounceback today wouldn't be a big surprise.

But this much is clear: Many investors have more in stocks than they really need -- and that extra risk could come back to haunt them.

-- Getting ahead. To understand what's at issue, imagine it is the beginning of 2006 and you have $300,000 in retirement savings.

That money is split between 70% stocks and 30% bonds. You figure your stocks will return 8% a year over the long haul and your bonds might clock 5%. Meanwhile, over the next 12 months, you're aiming to sock away 12% of your $80,000 salary, or $9,600.

If you got what you expected, you would have had some $331,000 at year-end 2006. But as it turns out, while your bonds eked out 4% last year, your stocks leapt 16%, so you finished the year with more than $347,000. Result: You're over $16,000 ahead of where you expected to be.

The standard advice is that you should rebalance back to your 70% stock-30% bond mix, and I think that's a fine strategy. What if you're tempted to leave your stocks to run?

My contention: If you're going to start fooling around with your asset allocation, you should reduce your stocks below 70%, not overweight them. After all, you are now closer to your retirement goal than you expected -- which suggests you don't need to take so much risk to accumulate your desired nest egg.

'Investing is never just about return,' says William Bernstein, an investment adviser in North Bend, Ore. 'It's also about controlling risk. If you've already won the game, what sense does it make to go on playing?'

-- Growing cautious. I can already hear the objections. If stocks usually beat bonds, why not own more? If you're ahead of schedule with your retirement savings, why not save less or retire earlier?

It could be that you'll do just fine with such strategies. But a little caution is probably in order. The fact is, the stock market doesn't generate returns in a vacuum. Instead, share-price appreciation is driven by economic growth and the resulting rise in corporate earnings.

True, over the short term, stock prices can race ahead of the economy. Maybe exuberant investors will bid up the stock market's price/earnings multiple. Maybe corporate profits will, for a year or two, grow faster than the economy.

But over the long haul, share-price gains will mirror economic growth. During the past 50 years, for instance, the Standard & Poor's 500-index has notched an average annual share-price gain of 7.1%, right in line with the 7.1% annual increase in gross domestic product. Tack on dividends, and you get a total return of 10.6%. The bottom line: We can't get outsized stock returns every year -- and periods of heady gains will inevitably be followed by stretches of modest performance.

-- Crying uncle. If you are more than 10 or 15 years from retirement, I wouldn't fret too much over the market's recent performance, including yesterday's big decline. Instead, stick with your stock allocation and continue socking away money like crazy.

But those already retired or close to quitting the work force should think carefully about how much money they need for retirement -- and whether they need to take so much risk, especially after the stellar gains of recent years. To see if you have enough money to carry you through a long retirement, try the two online calculators listed in the accompanying chart.

Even if you have plenty of money for retirement, you should probably continue holding at least 30% or 35% in stocks as part of a diversified portfolio. And arguably, you might go somewhat higher -- for the sake of your heirs. 'There comes a point when you have more than enough money and you take risk not for yourself, but for your beneficiaries,' Mr. Bernstein says.

Jonathan Clements