Behavioral bias definitions

Common behavioral biases
Behavioral bias in investment decision making

Cognitive bias in investment decision-making

We’ve compiled a list of the main unconscious biases and their influence on the way we invest and make financial decisions.

To understand the impact of cognitive bias on active management, download our free white paper by investment process expert, Eric Rovick. Written with an insider’s perspective, it offers practical steps for portfolio managers who want to recognise and manage bias in their daily investment processes.


When we rely too much on the first piece of information we came across when making a decision.

Availability Heuristic (aka Availability Bias)

A mental shortcut by which one overestimates the importance or likelihood of something based on how easily an example or instance comes to mind.

This bias is important because of its impact on how well we perceive risk. Of course, what we remember or how easily something comes to mind will be influenced by many things but media coverage is usually a big factor.

“People tend to assess the relative importance of issues by the ease with which they are retrieved from memory—and this is largely determined by the extent of coverage in the media. Frequently mentioned topics populate the mind even as others slip away from awareness…”.

Daniel Kahneman – Thinking, Fast and Slow (2011)

Bandwagon Effect

Believing something is true or correct because many other people do.

Blind Spot Bias

Demonstrated when we think we’re less prone to cognitive bias than those around us.

“People see themselves differently from how they see others. They are immersed in their own sensations, emotions, and cognitions at the same time that their experience of others is dominated by what can be observed externally.”

Emily Pronin – How We See Ourselves and How We See Others (2008)

Conjunction Fallacy

This representativeness heuristic is a tendency to assume that specific conditions are more probable than general ones.

Clustering Illusion

The tendency to overestimate the importance of small patterns or clusters found in a large amount of data.

Confirmation Bias

Also called Confirmatory Bias or Myside Bias, this is the tendency to search for, interpret, and remember information in a way that confirms their existing preconceptions. This unconscious bias makes it possible to miss findings or ignore evidence that could otherwise change our view.

“Now, there was a smart man, who did just about the hardest thing in the world to do. Charles Darwin used to say that whenever he ran into something that contradicted a conclusion he cherished, he was obliged to write the new finding down within 30 minutes. Otherwise his mind would work to reject the discordant information, much as the body rejects transplants. Man’s natural inclination is to cling to his beliefs, particularly if they are reinforced by recent experience–a flaw in our makeup that bears on what happens during secular bull markets and extended periods of stagnation.”

Warren Buffet in Fortune Magazine (2001)

Conservatism Bias

When we cling to an initial viewpoint even when there’s new information or evidence that challenges it.

The Curse of Knowledge

When knowledge of a topic diminishes our ability to think about it from a less-informed, but more neutral, perspective.

Disposition Effect

An expression of Loss Aversion, the Disposition Effect was identified and named by Hersh Shefrin and Meir Statman in 1985. It is the tendency common to both professional and amateur investors to hold on to losing investment positions for too long, whilst selling winners too soon.

Research into the investment impact of the Disposition Effect by Terrance Odean (Are Investors Reluctant to Realize Their Losses? – 1998) showed that winners that were sold outperformed losers that were retained by an average excess return of 3.4% per annum.

“Meir Statman and I… coined the term disposition effect as shorthand for the predisposition toward get-evenitis.”

Hersh Shefrin (2000)

Endowment Effect

When we consider an asset that we already own as more valuable than similar assets that we don’t.

The Framing Effect

Drawing different conclusions from the same information, depending on how or by whom that information is presented.

Gambler’s Fallacy

The belief that future probabilities are altered by past events. This bias is a product of “representativeness”, a psychological phenomenon that leads us to rely overly on heuristics (rules of thumb) or “stereotypical thinking” when making decisions or judgements.

Linked to the Hot-Hand Fallacy in Basketball, where observers predict a player will continue to play well because recent performance has been so good:

“….statistically, there is no such thing as a hot hand. This is not to say that we do not see streaks. We do see them, but the point is that they have no predictive power! The idea that streaks have predictive power is an illusion. The fact is, as a species, humans have very poor intuition about random processes, whether the process is coin tossing or whether it is three-point attempts in basketball. In particular, representativeness leads us to extrapolate recent performance.”

Hersh Shefrin, Behavioral Finance: Biases, Mean–Variance Returns, and Risk Premiums (2007)

Gratification Bias

The tendency to favor short-term gain over greater gain available in the long-term.

Herding Effect

The tendency to follow the actions of a larger group.

“Herd followers have a high probability of achieving average performance, but in exchange for safety from being much below average, they surrender their chance of being much above average.”

Howard Marks, Oaktree Capital Management (2006)

House Money Effect

The tendency to take on greater risks when investing with profits. The name is derived from the expression “playing with the house’s money.”

The IKEA Effect

This bias explains the tendency for people to place a disproportionately high value on objects that they partially created themselves, regardless of the quality of the end result.

In the original 2011 research, The IKEA effect: When labor leads to love, consumers assembled IKEA boxes, folded origami, and built Lego sets. Participants of the study saw their amateurish creations as similar in value to those created by experts and expected others to have the same view. The IKEA effect was only evident when the participants had successfully completed their assembly task; when they built and then destroyed their creations, or failed to complete it, the cognitive bias dissipated.

“The overvaluation that occurs as a result of the IKEA effect has implications for organizations more broadly, as a contributor to two key organizational pitfalls: sunk cost effects (Arkes and Blumer 1985; Staw 1981), which can cause managers to continue to devote resources to failing projects in which they have previously invested (Biyalogorsky, Boulding, and Staelin 2006), and the “not invented here” syndrome, in which managers refuse to use perfectly good ideas developed elsewhere in favor of their – sometimes inferior – internally-developed ideas.”

Norton, Mochon and Ariely (2011)

Illusion of Validity

Describes the tendency to overrate our ability to make accurate predictions, especially when analyzing data that presents a consistent pattern or tells a coherent story.

Information Bias

Sometimes we tend to seek information even when it does not affect action. Better decisions can often be made with less information – more is not always better.

Loss Aversion

The tendency for people to prefer avoiding losses than acquiring gains. Associated with Kahneman & Tversky’s Prospect Theory, the behavioral model that shows how people decide between alternatives when the probability of outcomes is unknown.

“In human decision-making, losses loom larger than gains.”

Kahneman and Tversky – Prospect Theory: An Analysis of Decision under Risk (1979)

Mental Accounting Bias

Also known as the “two-pocket theory”, this is when we divide our money into separate categories according to subjective criteria, such as where the money came from, or what we intend to use it for. In reality, money is fungible and one dollar is worth as much as the next, whatever its source or purpose. This bias, and its impact on how rational we are in our spending and investment decisions, represents a “fungibility violation”.

“Mr. and Mrs. J have saved $15,000 toward their dream vacation home. They hope to buy the home in five years. The money earns 10% in a money market account. They just bought a new car for $11,000 which they financed with a three-year car loan at 15%.”

Richard H. Thaler – Mental Accounting and Consumer Choice (1985)

Observational Selection Bias

The effect of suddenly noticing something we didn’t notice much before and wrongly deducing from this that its frequency has increased.

Observer Expectancy Effect

When a researcher anticipates a certain result and therefore unconsciously manipulates an experiment or misinterprets data in order to find it.

Optimism Bias

This is seen when we tend to overestimate the probability of positive outcomes and fail to acknowledge the potential for adverse consequences.

Outcome Bias

The tendency to judge a decision by its eventual outcome, rather than the quality of the decision when it was made. This behavioral tendency leads us to de-emphasize the events preceding an investment outcome, whilst overemphasizing the outcome.

“The fact that something worked doesn’t mean it was the result of a correct decision, and the fact that something failed doesn’t mean the decision was wrong. This is at least as true in investing as it is in sports.”

Howard Marks, Inspiration from the World of Sports Memo (2015)

Overconfidence Bias

When confidence in our own judgement is greater than the objective accuracy of those judgements.

Pessimism Bias

The tendency to focus on what can go wrong and overestimate the likelihood of negative events.

Reactive Devaluation

When we reject proposals that are potentially favorable to us just because they come from another party, opponent or rival.

Recency Bias

When people weigh recent events and observations more heavily than those in the past.

Regret Aversion

The tendency to avoid making decisions that we fear we could later regret.

Risk Compensation

Suggests that we adjust our behavior according to our perception of the risk level, becoming less careful when we feel safer and more cautious when the perceived risk level increases.

Status Quo Bias

Evident when people resist change and prefer things to stay the same or stick with previous decisions.

Sunk Cost Effect

The tendency to throw good money after bad. Can lead us to continue investing into a project based on our earlier decisions, rather than on its current objective merits or despite new evidence suggesting that the decision was probably wrong. Also called Irrational Escalation.

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