平均成本法：股市投資的不二選擇

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平均成本法：股市投資的不二選擇

2010年08月10日07:55

過去幾個月中﹐股市經歷了極度緊張的時期﹐經歷了今年良好的開局後﹐5月初股市開始下跌﹐期間“閃電崩盤”加劇了跌勢﹐這種情況一直延續到7月。

隨著股價下跌﹐有關股市調整的傳言變為熊市里到處彌漫的言論。有勇氣就投資吧﹐這是肯定的。最近股市隨著企業公佈一連串強勁的獲利報告而活躍起來。

從目前向後回溯（事後諸葛亮不好嗎？）﹐今年春天和夏初那些黯淡的日子﹐尤其是閃電崩盤後的幾週﹐現在看起來是投資的良好時段。雖然不是2009年3月觸及的幾十年年低點﹐但卻是差不多的低位。

近幾個月股市的動盪凸顯了長期投資者面臨的難題：何時是入市的良好時機？尤其是你有大量資金要投資的時候﹐比如有了獎金、遺產或出售房屋所得收益的時候。

一個流行的方法是平均成本法（dollar-cost-averaging）﹐這一方法非常簡單：你在一段時間內﹐每月將一部分資金投入股市（在此情況下﹐我們將市場定義為標準普爾500指數的情況）﹐這就是逐漸涉足股市﹐而不是將所有資金一次都投入股市。隨著股市波動﹐當股價下跌時﹐按照平均成本法投資將買入更多股票﹐而當股價上漲時﹐則買入的更少。

這跟從工資里扣除一部分錢、或將季度股息進行再投資的每月投資額有些不同﹐你是在定期向股市投入新錢﹐這對長期投資者來說是良好的自我要求﹐只要投資計劃是多元化的﹐包括的不僅是股票就好。

讓我們看看大量資金所面臨的進退兩難的局面吧。一次投入所有資金聽起來非常像是抓住了市場時機﹐而我們知道抓住市場時機幾乎是不可能的。鑒於投資的人有數千萬﹐一些局外人將在很長一段時間聲稱他們有市場時機的判斷能力﹐但那些人也常常翻船﹐就在你碰巧注意到的時候。

平均成本法會讓情況得好些嗎？讓我們從年初看看。如果你得到了8,000美元聖誕獎金﹐你是在一年的第一個交易日全都投到股市呢﹐還是在一年的前八個月每月投資1,000美元呢？

在8月5日股市收盤後﹐在1月將全部獎金一次性投入股市的投資者漲幅將約為2.2%﹐在8,000美元的初期股本上獲利173.60美元﹐而用平均成本法進行的投資表現稍好一些﹐漲幅為2.3%﹐獲利187.13美元。

原因在哪兒呢？投入全部資金的投資者在1月大舉買入時﹐股價相對較高﹐依平均成本法買入的投資者也一樣﹐但股市在7月跌向低點時﹐平均成本法的投資者還在買入﹐因此也以較低的水平買入﹐這是依平均成本法操作獲利稍多的原因。

平均成本法招來許多批評﹐舉例來說﹐如果股市上漲﹐立即投資是否明智？這些批評基本上說平均成本法披著華麗外衣﹐而實際卻是判斷市場時機﹐這些批評有一些道理。如果你在去年9月開始了上述買入股票的例子﹐平均成本法表現將落後﹐從2009年9月1日起是股市的低迷期。

其他人認為經紀商使用平均成本法以避開客戶可能發出的報怨：它不讓投資者在接近高點時買入﹐但也不會讓投資者抄底。隨著時間推移將投資資金分攤﹐將減少兩者出現的幾率。

但平均成本法確實有意義﹐尤其是在動盪的市場里﹐這似乎已越來越成為常態。隨著時間推移投資一些資金﹐可以確保你在股市下跌時買入更多股票﹐在股市上漲時買入更少。

許多投資者犯下了高買低賣的錯誤﹐高買是在股市大漲的時候買入﹐低賣是在人們都驚恐萬狀的時候賣出。平均成本法可以防範這些毀滅性的非理性行為。單是這一因素就是將其納入你投資方式的一個原因。

Dave Kansas


A Season, and Market, for Wading

2010年08月10日07:55


For the past several months, the stock market has gone on one of its white-knuckle jags. After a reasonably good start to the year, prices started skidding in early May with the so-called Flash Crash punctuating a decline that reached into July.

As prices went lower, talk of a correction morphed into bear-market chatter. A nervy time to invest, that's for sure. More recently, of course, stocks have perked up amid a sea of strong corporate profits.

Looking back from today (isn't hindsight wonderful?), those dark days of spring and early summer, especially the weeks after the Flash Crash, now look like pretty good times to have invested. Not as stark as the generational lows reached in March 2009, but lows all the same.

The volatile nature of recent months underscores the long-term investors' conundrum: When is the right time to get into the market, especially if you have a lump sum to invest, such as a bonus, inheritance or proceeds from a home sale?

One popular method involves dollar-cost averaging. The notion is elegantly simple: Rather than taking the plunge with all of your money at once, you invest a set amount in the market (in this case, we define the market as the Standard & Poor's 500-stock index) each month over a set period of time, thereby sort of wading into the market. As prices fluctuate, the dollar-cost averager will buy more of the market when prices are low, and less when prices are high.

This is modestly different from investing a set amount each month as part of a payroll deduction plan or a quarterly dividend reinvestment plan. You are putting fresh money into the market on a regular basis, something that is a good discipline for a long-term investor-as long as the investment plan is diversified to include more than just stocks.

But let's get back to the lump-sum dilemma. Putting it in all at once sounds suspiciously like market timing. And we know that timing the market is practically impossible. Given the tens of millions of people who invest, some outliers will get lucky for long enough to claim market-timing prowess, but those people often stumble just as they get noticed.

Does dollar-cost-averaging make things better? Let's look at things from the start of the year. If you had gotten an $8,000 Christmas bonus, would you have been better off investing it all at once on the first trading day of the year, or investing $1,000 a month over the first eight months?

After the market closed on Aug. 5, the investor who took the January plunge would have been up about 2.2%, or $173.60 on the initial $8,000. The dollar-cost averager would have fared fractionally better, with a 2.3% gain, or $187.13.

The reason? The plunger bought in January when the market was relatively expensive. The dollar-cost averager did, too, but also scooped up the market as it plunged toward lows in July, thereby buying at cheaper levels as well. That's where the dollar-cost averager gained an edge.

Dollar-cost averaging has plenty of critics. For instance, if the market goes up over time, doesn't it make sense to get the money invested right away? This criticism, which basically says dollar-cost averaging is market timing in fancy dress, has some merit. If you started the above example back in September of last year, the dollar-cost averager would come out behind, since Sept. 1, 2009, represented a low point for the stock market during the period.

Others argue that brokers use dollar-cost averaging to ward off the potential wrath of their clients: It prevents the investors from buying at a near-term top -- but it could also rob them of buying at a bottom. Spreading the investment of a lump sum over time diminishes the likelihood of both.

Still, dollar-cost averaging does make sense, especially in volatile markets, which seem increasingly like the norm. Investing a set amount of money over time ensures that you will get more of the market when it is cheap and less of the market when it is expensive.

Many investors make the mistake of buying high-when things are going great-and selling low-when everybody's in a panic. Dollar-cost averaging guards against these damaging animal spirits. That alone is a good reason to have it in your investment quiver.

Dave Kansas