Behavioural finance, or the study of investor psychology, marries the psychology of decision-making with investors’ trading behaviour and asset pricing. Departures from rational decision-making emerge because individuals do not enjoy unlimited information-processing capabilities and instead rely on rules of thumb when making decisions under uncertainty. This leads to systematic cognitive errors and mispriced assets. But behavioural finance helps us to understand why certain market anomalies exist and persist.
Efficiencies and Inefficiencies
The efficient market hypothesis, introduced 30 years ago, argues that information is processed properly by investors and reflected in the price of assets instantaneously. By being rational, investors are expected to update their beliefs correctly upon receiving new information and, given those beliefs, make choices that are normatively acceptable to maximize their returns. Under this hypothesis, active management is unable to achieve superior returns to the market.
On the other hand, behavioural finance proponents acknowledge that investors are human beings who are subject to a range of emotions and information-processing errors that push them to make suboptimal trading decisions. This leads to mispriced assets and inefficient markets. Investors who understand and avoid these mistakes could exploit the resulting inefficiencies and end up earning excessive returns. With the discovery of market anomalies such as the value premium, the momentum effect and the post-earnings announcement drift, it is tempting to search for answers in human psychology to explain investors’ underreaction or overreaction.
Common Biases
David Hirshleifer (2001) believed most mistakes that individuals make can be traced to four common causes: self-deception (limits to learning), heuristic simplification (rules of thumb), emotions and social interaction.
Self-deception: Under this category, we observe overconfidence, the illusion of knowledge and the confirmation bias. How many of us are guilty of thinking we are better-than-average students, better-than-average drivers and better-than-average portfolio managers? While a majority of us think that way, the truth is, the math just does not work. We are simply overconfident.
The illusion of knowledge is the belief that the accuracy of our forecasts increases with more information. More information is not necessarily better information; it’s what you do with the information that matters. In fact, the dangerous thing about information overload is that it actually increases our confidence (overconfidence) but not necessarily our skills.
The confirmation bias is our habit of looking only for information that agrees with our pre-existing beliefs; it is our thirst for agreement. Because it feels good to have our opinions reflected back to us, we search for information that supports our views and ignore facts (or people) that conflict with our opinions.
Heuristics: With rules of thumb, individuals are subject to anchoring and representativeness. Anchoring is observed when someone’s initial expectations or prior probabilities are based on a starting point (an anchor), which is adjusted when new information arrives. While in theory, we should objectively consider the value of new information and arrive at a new predicted outcome, the fact is that we always start with an anchor first and then make adjustments. Investment professionals who entered the U.S. market in the mid-1990s could not believe the market was going anywhere but up before the turn of the century, whereas those who witnessed both the technology, media and telecom and the credit crunch crashes are a little more careful when assessing the relative valuation of the market nowadays.
Representativeness causes individuals to expect samples to be highly representative of the parent population from which they are drawn. People see trends and patterns in random events. They assign too much importance to extreme and strong new information and not enough to the information’s weight or statistical stability. For example, five spins of a roulette wheel ending on black does not mean red is due, just as five years of good earnings growth does not mean the company can sustain its competitive edge over the next five years. The sample is just too small to be highly representative.
Under the efficient market hypothesis, investors are rational decision-makers when faced with uncertainty. They weigh the value of each alternative separately, then choose the one with the highest expected return. On the other hand, in prospect theory—a positive model of judgment when faced with uncertainty—value is defined as a change in wealth around a reference point. For the same absolute amount, losses are felt with more pain than the corresponding joy of a gain. This is referred to as loss aversion. In addition, in the domain of gains, investors exhibit risk aversion. They prefer a certain gain over the possibility of a higher gain (e.g., they prefer a 100% chance of winning $3,000 over an 80% chance of winning $4,000).
In the domain of losses, however, investors become risk seekers. When faced with the certainty of a $3,000 loss or a higher but just as probable loss (80% probability of a $4,000 loss), they will go with the second option. The certainty effect gives more weight to the outcome, more joy for a certain gain and more pain for a certain loss. Interestingly enough, when probabilities are very low, the opposite occurs: humans become risk seekers for gains (what other explanation is there for purchasing lottery tickets?) and risk averse for losses (insurance premiums, anyone?).
| Confidence Breaker Information overload is not only overwhelming, it’s also dangerous. Too much information actually increases people’s confidence (overconfidence) but not necessarily their skills. This has been proven in Stuart Oskamp’s classic experiment (1965), showing how confidence increases as people gain more knowledge. Thirty-two judges (psychologists and graduate students) were asked to read background information about a case of adolescent maladjustment, divided into four stages. After each stage, they had to answer 25 multiple choice questions involving personal judgments. The results confirmed the hypothesis that as more information was received by the judges, their confidence level would rise markedly and steadily. However, the accuracy of their conclusions would quickly reach a ceiling. (See pdf for figure) |
Common Market Anomalies
Investors’ overreaction in extrapolating a firm’s recent earnings growth and pushing the stock’s price too high or too low has been linked to the representativeness bias. Based on relatively small samples of earnings releases, investors will tend to become too bearish on a stock that has been performing poorly, pushing its price down until it becomes relatively cheap and has a better chance, going forward, to outperform its peers (the value premium).
The momentum and earnings surprise anomalies are both seen as underreaction to news. Momentum is the serial correlation of returns that has been observed in various parts of the world, whereby past winners/losers outperform/underperform their peers in the following one to 12 months.
Earnings surprise is the post-earnings announcement drift in the stock price that occurs when a company delivers earnings that exceed/miss the consensus (the surprise) and continues to outperform/underperform (the drift) for subsequent periods as long as six months into the future.
Conservatism, whereby we overweight our prior views and underweight new evidence, and anchoring (on past prices) can help us explain why the release of new information is reflected only in prices over time instead of immediately, as the proponents of the efficient market hypothesis believe.