Cathy Pareto 2016年8月13日
當涉及錢和投資，我們不總是像我們想的那麼理性，這就是為什麼有一個整體的領域來研究我們時常的奇怪行為。你適合做一個投資者嗎？行為金融學的理論和研究可能幫助你回答這一問題。
行為金融學：理性假設的質疑
許多經濟理論都基於這樣一個理念，即個人行為是以理性的方式進行的並且所有現存信息都是嵌入到投資過程裡的。這一理念是市場假說有效性的關鍵。
但是質疑這一假說的研究人員發現有證據表明理性行為並不向我們認為那樣的普遍存在。行為金融學試圖理解和解釋在決定形成過程中人類感情是怎樣影響投資者的。你會對他們的發現感到震驚。
事實
2001年，金融服務研究公司Dalbar發佈了一篇名為“投資者行為量化分析”的研究報告，其結論是普通投資者不能獲得市場指數的回報。報告發現在截止到2000年12月的17年時間裡，標準普爾的年均回報率為16.29%，而傳統股票投資者的年均回報率在這期間僅為5.32%，差異驚人的達到9%。
研究還發現，在同一時期，固定收益投資者的年均收益僅為6.08%，而同期的長期政府債務指數收益則高達11.83%。
在2015年發表的相同報告中，Dalbar再次總結到普通投資者不能獲得市場指數等額的回報。研究發現普通證券投資基金投資者獲得的回報比標準普爾500低8.19%。更廣泛市場回報是普通股票投資基金投資者獲得回報的兩倍多。
普通固定收益共同基金投資獲得的回報也比債券市場低4.81%。
為什麼會發生這樣的現象呢？可能會有無數個解釋。
後悔理論
後悔理論解釋人們意識到判斷錯誤後的情緒反應。面對抛售一種持有股票的前景時，投資者的情緒將會受到他們購買股票時價格的影響。
因此，他們把拒絕出售該股票作為避免後悔做出糟糕投資和面對尴尬虧損報告的方式。我們都會犯錯，不是嗎？
在考慮出售一支股票時投資者真正應該問自己的是：“如果這支股票已經清算，我重新購買會出現什麼結果呢，我是否應該對其進行再次投資？”
如果答案是否定的，那麼出售的時間已經到了。另外，這個結果是後悔購買一支虧損股票並且後悔沒有在事實清晰的表明這個投資是錯誤時沒有出售，這是一個惡性循環，避免後悔導致了更多的後悔。
後悔理論還適用於投資者發現他們曾經打算購買的股票價格上漲時。一些投資者為了避免這種後悔出現根據大衆觀點購買股票而且只購買那些旁人也購買的股票，用“大家都在這麼做”來解釋他們的決定。
奇怪的是，許多人在大多數人都持有的流行股票上虧損時的尴尬要比在那麼不知名和不受歡迎股票上虧損時小的多。
心理價格
人類傾向於把特殊事件在心裡計算價格，這些心理價格的有時候對我們行為的影響會比事件本身大得多。
舉例來說，你想去當地劇院看演出，門票是20塊。當你到了之後突然發現你丢了20快，那麼你還會去買票嗎？
行為金融學發現在這種情況下88%的會去買票。現在讓我們假設你提前花20塊買了票。當你到門口的時候發現你的票落家了。你會再花20塊另買一張票嗎？
只有40%的受調查對象會另買一張。然而，在兩種情況下你都會支出40塊。情況不同，錢的數量相同，心理價格不一樣。這是不是很蠢？
能最好诠釋心理價格的投資案例是猶豫出售一種曾經達到巨大收益但是現在收益卻一般的投資。在經濟繁榮和牛市市場中，人們習慣於健康的字面收益。當市場修正使投資的淨值降低，他們會猶豫是否以降低的利潤出售。他們會形成曾經獲得巨大收益的心理價格，導致等待回到那個收益水平的價格。
前景理論/損失厭惡理論
不用咨詢心理醫生我們也知道相對於不確定回報人們更喜歡確定投資回報，我們在承擔額外風險時想要獲得回報。這是很合理的。
這裡有一點很奇怪。前景理論認為人們對收益和虧損的感情程度不一樣。人們在面對虧損前景時的緊張程度比等值的收益前景時的高興程度大。
當報告客戶的投資組合獲得50萬收益時，投資顧問的電話不一定會響個不停。但是我們可以確定如果是虧損50萬，他的電話一定會被打爆。等值的虧損獲得的關註程度永遠比收益大，錢進入你的口袋後價值就會發生變化。
前景理論也解釋了為什麼投資者繼續持有虧損的股票，因為相對於現實的收益，人們更樂意承受更多的風險。因為這個原因，投資者甯願呆在股票的高風險位置，期待價格反彈。接連失敗的賭徒會出現類似的行為，他們會加倍下註以希望收回原來的虧損。
因此，盡管我們希望對承擔的風險獲得理性回報，我們通常會傾向於把我們持有某些東西的價格看得高於我們原來想要出售的價格。
厭惡虧損理論指出了投資者出售盈利股票繼續持有虧損股票的另一個原因，他們相信現在虧損的股票將來的表現可能好於現在盈利的股票。調查表名，流入表現良好共同基金的資金要比流出表現不佳的對沖基金的資金要頻繁的多。
錨定
由於缺乏更好或者新的信息，投資者通常假設市場價格是正確價格。人們更傾向於相信最近的市場觀點、看法和事件，並且錯誤推斷區別於歷史、長期平均值和概率的最近趨勢。
在牛市中，投資者決定通常會受到價格錨的影響，這些價格錨是是被視為意義重大的價格，原因是他們是最近價格。這使得過去的決定回報和投資者決定不相關。
過度/過低反應
當市場上升時投資變得樂觀，會假設這一趨勢會持續。相反，投資者在市場下跌期間會變得非常悲觀。這是錨定或者過分重視最近事件而忽視歷史數據的結果，這是一種過度反應，使導致市場事件的壞消息出現時價格下跌太多而好消息則上漲太多。
在樂觀的高峰期，投資者湧向那些超過其内在價值的股票。什麼時候開始投資零收益和無限市盈率的股票的決定變得合理了呢？
對市場事件過度/過低反應可能會導致市場恐慌和崩潰。
過分自信
人們通常認為自己的能力高於平均水平。他們通常高估他們的知識和其他關於知識的能力。
許多投資者認為他們可以不斷的進行波段操作，然而事實上有大量的證據表明他們是錯誤的。過分自信導致過多交易，交易成本使利潤降低。
反面意見：非理性行為是異常現象嗎？
正如我們之前提到的，行為金融學理論與傳統金融觀點直接沖突。他們都試圖解釋投資者行為和這些行為的暗示。那麼誰是正確的呢？
和行為金融學沖突最激烈的是Eugene Fama和Ken French提出的有效市場假說（EMH）。他們的理論認為市場價格能否有效包含所有現有信息取決於投資者是否理性。
EMH的支持者認為行為金融學只能解釋短期異常事件或者幾率性結果，而在長期中這些異常將消失並回歸到市場有效性假說中。
因此，可能沒有充足的證據表明市場有效性假說應該被抛棄，因為過去的經驗表明市場會在長期過程中糾正自己。在其《以上帝為對手: 風險傳奇(概率與經濟)》一書中，Peter Bernstein對辯論中利害攸關的問題做了很好的闡述：“重要的是了解市場不按傳統經典模式設想的行事，有許多證據表明，行為金融學關於投資者非理性的觀點與事實一致，但是我不知道你能怎樣利用這些信息管理資金。我仍然不相信有人能不利用它一直賺錢。”
總結
行為金融學當然反映了一些嵌入投資系統的觀點。行為主義者會說投資者通常會進行不理性行為產生無效市場和對股票錯誤定價，更不用說獲得賺錢機會。
這在一時可能是正確的，但是不斷揭露這些無效性是非常困難的。問題仍然在於這些行為金融學理論是否能被用來有效的管理你的資金。
也就是說，投資者是他們自己最大的敵人。試圖看透市場在長期中不會產生回報。事實上，這通常會導致奇怪的非理性行為，從而引起你的資產貶值。
實行一個深思熟慮的策略並且堅持下去可以幫助你避免這些常見的錯誤。
Understanding Investor Behavior
By Cathy Pareto | Updated August 13, 2016 — 6:08 AM EDT
When it comes to money and investing, we're not always as rational as we think we are - which is why there's a whole field of study that explains our sometimes-strange behavior. Where do you, as an investor, fit in? Insight into the theory and findings of behavioral finance may help you answer this question.
Behavioral Finance: Questioning the Rationality Assumption
Much economic theory is based on the belief that individuals behave in a rational manner and that all existing information is embedded in the investment process. This assumption is the crux of the efficient market hypothesis.
But researchers questioning this assumption have uncovered evidence that rational behavior is not always as prevalent as we might believe. Behavioral finance attempts to understand and explain how human emotions influence investors in their decision-making process. You'll be surprised at what they have found.
The Facts
In 2001 Dalbar, a financial-services research firm, released a study entitled "Quantitative Analysis of Investor Behavior", which concluded that average investors fail to achieve market-index returns. It found that in the 17-year period to December 2000, the S&P 500 returned an average of 16.29% per year, while the typical equity investor achieved only 5.32% for the same period - a startling 9% difference!
It also found that during the same period, the average fixed-income investor earned only a 6.08% return per year, while the long-term Government Bond Index reaped 11.83%.
In its 2015 version of the same publication, Dalbar again concluded that average investors fail to achieve market-index returns. It found that "the average equity mutual fund investor underperformed the S&P 500 by a wide margin of 8.19%. The broader market return was more than double the average equity mutual fund investor’s return. (13.69% vs. 5.50%)."
Average fixed income mutual funds investors also under performed at a 4.18% under the bond market.
Why does this happen? There are a myriad of possible explanations.
Regret Theory
Fear of regret, or simply regret, theory deals with the emotional reaction people experience after realizing they've made an error in judgment. Faced with the prospect of selling a stock, investors become emotionally affected by the price at which they purchased the stock.
So, they avoid selling it as a way to avoid the regret of having made a bad investment, as well as the embarrassment of reporting a loss. We all hate to be wrong, don't we?
What investors should really ask themselves when contemplating selling a stock is, "What are the consequences of repeating the same purchase if this security were already liquidated and would I invest in it again?"
If the answer is "no", it's time to sell; otherwise, the result is regret of buying a losing stock and the regret of not selling when it became clear that a poor investment decision was made - and a vicious cycle ensues where avoiding regret leads to more regret.
Regret theory can also hold true for investors when they discover that a stock they had only considered buying has increased in value. Some investors avoid the possibility of feeling this regret by following the conventional wisdom and buying only stocks that everyone else is buying, rationalizing their decision with "everyone else is doing it".
Oddly enough, many people feel much less embarrassed about losing money on a popular stock that half the world owns than about losing on an unknown or unpopular stock.
Mental Accounting
Humans have a tendency to place particular events into mental compartments, and the difference between these compartments sometimes impacts our behavior more than the events themselves.
Say, for example, you aim to catch a show at the local theater and tickets are $20 each. When you get there you realize you've lost a $20 bill. Do you buy a $20 ticket for the show anyway?
Behavior finance has found that roughly 88% of people in this situation would do so. Now, let's say you paid for the $20 ticket in advance. When you arrive at the door, you realize your ticket is at home. Would you pay $20 to purchase another?
Only 40% of respondents would buy another. Notice, however, that in both scenarios you're out $40: different scenarios, same amount of money, different mental compartments. Pretty silly, huh?
An investing example of mental accounting is best illustrated by the hesitation to sell an investment that once had monstrous gains and now has a modest gain. During an economic boom and bull market, people get accustomed to healthy, albeit paper, gains. When the market correction deflates investor's net worth, they're more hesitant to sell at the smaller profit margin. They create mental compartments for the gains they once had, causing them to wait for the return of that gainful period.
Prospect/Loss-Aversion Theory
It doesn't take a neurosurgeon to know that people prefer a sure investment return to an uncertain one - we want to get paid for taking on any extra risk. That's pretty reasonable.
Here's the strange part. Prospect theory suggests people express a different degree of emotion towards gains than towards losses. Individuals are more stressed by prospective losses than they are happy from equal gains.
An investment advisor won't necessarily get flooded with calls from her client when she's reported, say, a $500,000 gain in the client's portfolio. But, you can bet that phone will ring when it posts a $500,000 loss! A loss always appears larger than a gain of equal size - when it goes deep into our pockets, the value of money changes.
Prospect theory also explains why investors hold onto losing stocks: people often take more risks to avoid losses than to realize gains. For this reason, investors willingly remain in a risky stock position, hoping the price will bounce back. Gamblers on a losing streak will behave in a similar fashion, doubling up bets in a bid to recoup what's already been lost.
So, despite our rational desire to get a return for the risks we take, we tend to value something we own higher than the price we'd normally be prepared to pay for it.
The loss-aversion theory points to another reason why investors might choose to hold their losers and sell their winners: they may believe that today's losers may soon outperform today's winners. Investors often make the mistake of chasing market action by investing in stocks or funds which garner the most attention. Research shows that money flows into high-performance mutual funds more rapidly than money flows out from funds that are underperforming.
Anchoring
In the absence of better or new information, investors often assume that the market price is the correct price. People tend to place too much credence in recent market views, opinions and events, and mistakenly extrapolate recent trends that differ from historical, long-term averages and probabilities.
In bull markets, investment decisions are often influenced by price anchors, which are prices deemed significant because of their closeness to recent prices. This makes the more distant returns of the past irrelevant in investors' decisions.
Over-/Under-Reacting
Investors get optimistic when the market goes up, assuming it will continue to do so. Conversely, investors become extremely pessimistic during downturns. A consequence of anchoring, or placing too much importance on recent events while ignoring historical data, is an over- or under-reaction to market events which results in prices falling too much on bad news and rising too much on good news.
At the peak of optimism, investor greed moves stocks beyond their intrinsic values. When did it become a rational decision to invest in stock with zero earnings and thus an infinite price-to-earnings ratio (think dotcom era, circa year 2000)?
Extreme cases of over- or under-reaction to market events may lead to market panics and crashes.
Overconfidence
People generally rate themselves as being above average in their abilities. They also overestimate the precision of their knowledge and their knowledge relative to others.
Many investors believe they can consistently time the market, but in reality there's an overwhelming amount of evidence that proves otherwise. Overconfidence results in excess trades, with trading costs denting profits.
Counterviews: Is Irrational Behavior an Anomaly?
As we mentioned earlier, behavioral finance theories directly conflict with traditional finance academics. Each camp attempts to explain the behavior of investors and implications of that behavior. So, who's right?
The theory that most overtly opposes behavioral finance is the efficient market hypothesis (EMH), associated with Eugene Fama (Univ. Chicago) & Ken French (MIT). Their theory that market prices efficiently incorporate all available information depends on the premise that investors are rational.
EMH proponents argue that events like those dealt with in behavioral finance are just short-term anomalies, or chance results, and that over the long term these anomalies disappear with a return to market efficiency.
Thus, there may not be enough evidence to suggest that market efficiency should be abandoned since empirical evidence shows that markets tend to correct themselves over the long term. In his book "Against the Gods: The Remarkable Story of Risk" (1996), Peter Bernstein makes a good point about what's at stake in the debate:
"While it is important to understand that the market doesn't work the way classical models think - there is a lot of evidence of herding, the behavioral finance concept of investors irrationally following the same course of action - but I don't know what you can do with that information to manage money. I remain unconvinced anyone is consistently making money out of it."
Conclusion
Behavioral finance certainly reflects some of the attitudes embedded in the investment system. Behaviorists will argue that investors often behave irrationally, producing inefficient markets and mispriced securities - not to mention opportunities to make money.
That may be true for an instant, but consistently uncovering these inefficiencies is a challenge. Questions remain over whether these behavioral finance theories can be used to manage your money effectively and economically.
That said, investors can be their own worst enemies. Trying to out-guess the market doesn't pay off over the long term. In fact, it often results in quirky, irrational behavior, not to mention a dent in your wealth.
Implementing a strategy that is well thought out and sticking to it may help you avoid many of these common investing mistakes.
本文翻譯由兄弟財經提供
文章來源：http://www.investopedia.com/articles/05/032905.asp?rp=i