What Is Cognitive Bias?

Cognitive biases as systematic error in thinking and behavior outline diagram. Psychological mindset feeling with non logic judgment effects vector illustration.

Take-home Messages

  • Cognitive biases are unconscious errors in thinking that arise from problems related to memory, attention, and other mental mistakes.
  • These biases result from our brain’s efforts to simplify the incredibly complex world in which we live.
  • Confirmation bias, hindsight bias, self-serving bias, anchoring bias, availability bias, the framing effect, and inattentional blindness are some of the most common examples of cognitive bias. Another example is the false consensus effect.
  • Cognitive biases have direct implications on our safety, our interactions with others, and the way we make judgments and decisions in our daily lives.
  • Although these biases are unconscious, there are small steps we can take to train our minds to adopt a new pattern of thinking and mitigate the effects of these biases.

Have you ever been so busy talking on the phone that you don’t notice the light has turned green and it is your turn to cross the street?

Have you ever shouted, “I knew that was going to happen!” after your favorite baseball team gave up a huge lead in the ninth inning and lost?

Or have you ever found yourself only reading news stories that further support your own opinion?

These are just a few of the many instances of cognitive bias that we experience every day of our lives. But before we dive into these different biases, let’s backtrack a bit first and define what bias even is.

What is Cognitive Bias?

A cognitive bias is a subconscious error in thinking that leads you to misinterpret information from the world around you and affects the rationality and accuracy of decisions and judgments.

Biases are unconscious and automatic processes designed to make decision-making quicker and more efficient. Cognitive biases can be caused by many different things, such as heuristics (mental shortcuts), social pressures, and emotions.

Broadly speaking, bias is a tendency to lean in favor of or against a person, group, idea, or thing, usually in a way that is unfair. Biases are natural — they are a product of human nature — and they don’t simply exist in a vacuum or in our minds — they affect the way we make decisions and act.

In psychology, there are two main branches of biases: conscious and unconscious. Conscious bias, or explicit bias, is intentional — you are aware of your attitudes and the behaviors that result from them (Lang, 2019).

Explicit bias can be good because it helps provide you with a sense of identity and can lead you to make good decisions (for example, being biased towards healthy foods).

However, these biases can often be dangerous when they take the form of conscious stereotyping.

On the other hand, unconscious bias, or cognitive bias, represents a set of unintentional biases — you are unaware of your attitudes and behaviors resulting from them (Lang, 2019).

Cognitive bias is often a result of your brain’s attempt to simplify information processing — we receive roughly 11 million bits of information per second. Still, we can only process about 40 bits of information per second (Orzan et al., 2012).

Therefore, we often rely on mental shortcuts (called heuristics) to help make sense of the world with relative speed. As such, these errors tend to arise from problems related to thinking: memory, attention, and other mental mistakes.

Cognitive biases can be beneficial because they do not require much mental effort and can allow you to make decisions relatively quickly, but like conscious biases, unconscious biases can also take the form of harmful prejudice that serves to hurt an individual or a group.

And although it may feel like there has been a recent rise of unconscious bias, especially in the context of police brutality and the Black Lives Matter movement, this is not a new phenomenon.

The History of Cognitive Bias

The term cognitive bias was first coined in the 1970s by Israeli psychologists Amos Tversky and Daniel Kahneman, who used this phrase to describe people’s flawed patterns of thinking in response to judgment and decision problems (Tversky & Kahneman, 1974).

Tversky and Kahneman’s research program, the heuristics and biases program, investigated how people make decisions given limited resources (for example, limited time to decide which food to eat or limited information to decide which house to buy).

As a result of these limited resources, people are forced to rely on heuristics, or quick mental shortcuts, to help make their decisions.

Tversky and Kahneman wanted to understand the specific biases that are associated with this judgment and decision-making process.

In order to do so, the two researchers relied on a research paradigm that presented participants with some type of reasoning problem that had a computed normative answer (they used probability theory and statistics to compute the expected answer).

Participants’ actual responses were then compared with the predetermined solution to reveal the systematic deviations that occurred in the mind.

After running several experiments with countless reasoning problems, the researchers were able to identify numerous norm violations that result when our minds rely on these cognitive biases to make decisions and judgments (Wilke & Mata, 2012).


Thanks to Tversky and Kahneman (and several other psychologists who have paved the way), we now have an existing dictionary of our cognitive biases.

Again, these biases occur as an attempt to simplify the complex world and make information processing faster and easier. This section will dive into some of the most common forms of cognitive bias.

Confirmation Bias

Confirmation bias refers to the tendency to interpret new information as confirmation of your preexisting beliefs and opinions.

Real-World Examples

Since Watson’s 1960 experiment, real-world examples of confirmation bias have gained attention.

This form of bias often seeps into the research world itself when psychologists selectively interpret data or ignore unfavorable data to produce results that support their initial hypothesis.

Confirmation bias is also incredibly pervasive on the internet, particularly with social media. We tend to read online news articles that support our beliefs and fail to seek out sources that challenge them.

Various social media platforms, such as Facebook, help reinforce our confirmation bias by feeding us stories that we are likely to agree with – further pushing us down these echo chambers of political polarization.

Some examples of confirmation bias are especially harmful, specifically in the context of the law. For example, a detective may identify a suspect early in an investigation and then seek out confirming evidence and downplay falsifying evidence.


The confirmation bias dates back to 1960 when Peter Wason challenged participants to identify a rule applying to triples of numbers.

People were first told that the sequence 2, 4, 6 fit the rule, and they then had to generate triples of their own and were told whether that sequence fits the rule. The rule was simple: any ascending sequence.

But not only did participants have an unusually difficult time realizing this and instead devised overly-complicated hypotheses, they also only generated triples that confirmed their preexisting hypothesis (Wason, 1960).


But why does confirmation bias occur? It’s partially due to the effect of desire on our beliefs. In other words, certain desired conclusions (ones that support our beliefs) are more likely to be processed by the brain and labeled as true (Nickerson, 1998).

This motivational explanation is often coupled with a more cognitive theory.

The cognitive explanation argues that because our minds can only focus on one thing at a time, it is hard to parallel process (see information processing for more information) alternate hypotheses, so, as a result, we only process the information that aligns with our beliefs (Nickerson, 1998).

Another theory explains confirmation bias as a way of enhancing and protecting our self-esteem.

As with the self-serving bias (see more below), our minds choose to reinforce our preexisting ideas because being right helps preserve our sense of self-esteem, which is important for feeling secure in the world and maintaining positive relationships (Casad, 2019).

Although confirmation bias has obvious consequences, you can still work towards overcoming it by being open-minded and willing to look at situations from a different perspective than you might be used to (Luippold et al., 2015).

Even though this bias is unconscious, training your mind to become more flexible in its thought patterns will help mitigate the effects of this bias.

Hindsight Bias

Hindsight bias refers to the tendency to perceive past events as more predictable than they actually were (Roese & Vohs, 2012). There are both cognitive and motivational explanations for why we ascribe so much certainty to knowing the outcome of an event only once the event is completed.

 Hindsight Bias Example

Real-World Examples

When sports fans know the outcome of a game, they often question certain decisions coaches make that they otherwise would not have questioned or second-guessed.

And fans are also quick to remark that they knew their team was going to win or lose, but, of course, they only make this statement after their team actually did win or lose.

Although research studies have demonstrated that the hindsight bias isn’t necessarily mitigated by pure recognition of the bias (Pohl & Hell, 1996).

You can still make a conscious effort to remind yourself that you can’t predict the future and motivate yourself to consider alternate explanations.

It’s important to do all we can to reduce this bias because when we are overly confident about our ability to predict outcomes, we might make future risky decisions that could have potentially dangerous outcomes.


Building on Tversky and Kahneman’s growing list of heuristics, researchers Baruch Fischhoff and Ruth Beyth-Marom (1975) were the first to directly investigate the hindsight bias in the empirical setting.

The team asked participants to judge the likelihood of several different outcomes of former U.S. president Richard Nixon’s visit to Beijing and Moscow.

After Nixon returned back to the states, participants were asked to recall the likelihood of each outcome they had initially assigned.

Fischhoff and Beyth found that for events that actually occurred, participants greatly overestimated the initial likelihood they assigned to those events.

That same year, Fischhoff (1975) introduced a new method for testing the hindsight bias – one that researchers still use today.

Participants are given a short story with four possible outcomes, and they are told that one is true. When they are then asked to assign the likelihood of each specific outcome, they regularly assign a higher likelihood to whichever outcome they have been told is true, regardless of how likely it actually is.

But hindsight bias does not only exist in artificial settings. In 1993, Dorothee Dietrich and Matthew Olsen asked college students to predict how the U.S. Senate would vote on the confirmation of Supreme Court nominee Clarence Thomas.

Before the vote, 58% of participants predicted that he would be confirmed, but after his actual confirmation, 78% of students said that they thought he would be approved – a prime example of the hindsight bias. And this form of bias obviously extends beyond the research world.


From the cognitive perspective, hindsight bias may result from distortions of memories of what we knew or believed to know before an event occurred (Inman, 2016).

It is easier to recall information that is consistent with our current knowledge, so our memories become warped in a way that agrees with what actually did happen.

Motivational explanations of the hindsight bias point to the fact that we are motivated to live in a predictable world (Inman, 2016).

When surprising outcomes arise, our expectations are violated, and we may experience negative reactions as a result. Thus, we rely on the hindsight bias to avoid these adverse responses to certain unanticipated events and reassure ourselves that we actually did know what was going to happen.

Self-Serving Bias

Self-serving bias refers to the tendency to take personal responsibility for positive outcomes and blame external factors for negative outcomes.

You would be right to ask how this is similar to the fundamental attribution error (Ross, 1977), which identifies our tendency to overemphasize internal factors for other people’s behavior while attributing external factors to our own.

The distinction is that the self-serving bias is concerned with valence. That is, how good or bad an event or situation is. And it is also only concerned with events for which you are the actor.

In other words, if a driver cuts in front of you as the light turns green, the fundamental attribution error might cause you to think that they are a bad person and not consider the possibility that they were late for work.

On the other hand, the self-serving bias is exercised when you are the actor. In this example, you would be the driver cutting in front of the other car, which you would tell yourself is because you are late (an external attribution to a negative event) as opposed to it being because you are a bad person.

Real-World Examples

From sports to the workplace, self-serving bias is incredibly common. For example, athletes are quick to take responsibility for personal wins, attributing their successes to their hard work and mental toughness, but point to external factors, such as unfair calls or bad weather, when they lose (Allen et al., 2020).

In the workplace, people attribute internal factors when they have hired for a job but external factors when they are fired (Furnham, 1982). And in the office itself, workplace conflicts are given external attributions, and successes, whether it be a persuasive presentation or a promotion, are awarded internal explanations (Walther & Bazarova, 2007).

Additionally, self-serving bias is more prevalent in individualistic cultures, which place an emphasis on self-esteem levels and individual goals, and it is less prevalent among individuals with depression (Mezulis et al., 2004), who are more likely to take responsibility for negative outcomes.

Overcoming this bias can be difficult because it is at the expense of our self-esteem. Nevertheless, practicing self-compassion – treating yourself with kindness even when you fall short or fail – can help reduce the self-serving bias (Neff, 2003).


The leading explanation for why the self-serving bias occurs is that it is a way of protecting our self-esteem (similar to one of the explanations for the confirmation bias).

We are quick to take credit for positive outcomes and divert the blame for negative ones as a way of boosting and preserving our individual ego, which is necessary for confidence and healthy relationships with others (Heider, 1982).

Another theory argues that self-serving bias occurs when surprising events arise. When certain outcomes run counter to our expectations, we ascribe external factors, but when outcomes are in line with our expectations, we attribute internal factors (Miller & Ross, 1975).

An extension of this theory asserts that we are naturally optimistic, so negative outcomes come as a surprise and receive external attributions as a result.

Anchoring Bias

Anchoring bias is closely related to the decision-making process. It occurs when we rely too heavily on either pre-existing information or the first piece of information (the anchor) when making a decision.

For example, if you first see a T-shirt that costs $1,000 and then see a second one that costs $100, you”re more likely to see the second shirt as cheap as you would if the first shirt you saw was $120. Here, the price of the first shirt influences how you view the second.

 Anchoring Bias Example

Real-World Examples

From sports to the workplace, self-serving bias is incredibly common. For example, athletes are quick to take responsibility for personal wins, attributing their successes to their hard work and mental toughness, but point to external factors, such as unfair calls or bad weather, when they lose (Allen et al., 2020).

In the workplace, people attribute internal factors when they have hired for a job but external factors when they are fired (Furnham, 1982). And in the office itself, workplace conflicts are given external attributions, and successes, whether it be a persuasive presentation or a promotion, are awarded internal explanations (Walther & Bazarova, 2007).

Additionally, self-serving bias is more prevalent in individualistic cultures, which emphasize self-esteem levels and individual goals, and it is less prevalent among individuals with depression (Mezulis et al., 2004), who are more likely to take responsibility for negative outcomes.

Overcoming this bias can be difficult because it is at the expense of our self-esteem. Nevertheless, practicing self-compassion – treating yourself with kindness even when you fall short or fail – can help reduce the self-serving bias (Neff, 2003).


There are multiple theories that seek to explain the existence of this bias.

One theory, known as anchoring and adjustment, argues that once an anchor is established, people insufficiently adjust away from it to arrive at their final answer, and so their final guess or decision is closer to the anchor than it otherwise would have been (Tversky & Kahneman, 1992).

And when people experience a greater cognitive load (the amount of information the working memory can hold at any given time; for example, a difficult decision as opposed to an easy one), they are more susceptible to the effects of anchoring.

Another theory, selective accessibility, holds that although we assume that the anchor is not a suitable answer (or a suitable price going back to the initial example) when we evaluate the second stimulus (or second shirt), we look for ways in which it is similar or different to the anchor (the price being way different), resulting in the anchoring effect (Mussweiler & Strack, 1999).

A final theory posits that providing an anchor changes someone’s attitudes to be more favorable to the anchor, which then biases future answers to have similar characteristics as the initial anchor.

Although there are many different theories for why we experience anchoring bias, they all agree that it affects our decisions in real ways (Wegner et al., 2001).


The first study that brought this bias to light was during one of Tversky and Kahneman’s (1974) initial experiments. They asked participants to compute the product of numbers 1-8 in five seconds, either as 1x2x3… or 8x7x6…

Participants did not have enough time to calculate the actual answer, so they had to make an estimate based on their first few calculations.

They found that those who computed the small multiplications first (i.e., 1x2x3…) gave a median estimate of 512, but those who computed the larger multiplications first gave a median estimate of 2,250 (although the actual answer is 40,320).

This demonstrates how the initial few calculations influenced the participant’s final answer.

Availability Bias

Availability bias (also commonly referred to as the availability heuristic ) refers to the tendency to think that examples of things that readily come to mind are more common than what is actually the case.

In other words, information that comes to mind faster influences the decisions we make about the future. And just like with the hindsight bias, this bias is related to an error of memory.

But instead of it being a fabrication of memory, it is an overemphasis on a certain memory.

In the workplace, if someone is being considered for a promotion but their boss recalls one bad thing that happened years ago but left a lasting impression, that one event might have an outsized influence on the final decision.

Another common example is someone buying lottery tickets because the lifestyle and benefits that come with winning are more readily available in mind (and the potential emotions that are associated with winning or seeing other people win) than the complex probability calculation of actually winning the lottery (Cherry, 2019).

A final common example that is used to demonstrate the availability heuristic describes how seeing several television shows or news reports about shark attacks (or anything that is sensationalized by the news, such as serial killers or plane crashes) might make you think that this incident is relatively common even though it is not at all.

Regardless, this way of thinking might make you less inclined to go in the water the next time you go to the beach (Cherry, 2019).


As with most cognitive biases, the best way to overcome them is by recognizing the bias and being more cognizant of your thoughts and decisions.

And because we fall victim to this bias when our brain relies on quick mental shortcuts in order to save time, slowing down our thinking and decision-making process is a crucial step to mitigating the effects of the availability heuristic.

Researchers think this bias occurs because the brain is constantly trying to minimize the effort necessary to make decisions, and so we rely on certain memories – ones that we can recall more easily – instead of having to endure the complicated task of calculating statistical probabilities.

There are two main types of memories that are easier to recall: 1) those that more closely align with the way we see the world and 2) those that evoke more emotion and leave a more lasting impression.


This first type of memory was identified back in 1973, when Tversky and Kahneman, our cognitive bias pioneers, conducted a study in which they asked participants if more words begin with the letter K or if more words have K as their third letter.

Although many more words have K as their third letter, 70% of participants said that more words begin with K because the ability to recall this is not only easier, but it more closely aligns with the way they see the world (knowing the first letter of any word is infinitely more common than the third letter of any word).

In terms of the second type of memory, the same duo ran an experiment in 1983, 10 years later, where half the participants were asked to guess the likelihood of a massive flood would occur somewhere in North America, and the other half had to guess the likelihood of a flood occurring due to an earthquake in California.

Although the latter is much less likely, participants still said that this would be much more common because they were able to recall specific, emotionally charged events of earthquakes hitting California, largely due to the news coverage that they receive.

Together, these studies highlight how memories that are easier to recall greatly influence our judgments and perceptions about future events.

Inattentional Blindness

A final popular form of cognitive bias is inattentional blindness. This occurs when a person fails to notice a stimulus that is in plain sight because their attention is directed elsewhere.

For example, while driving a car you might be so focused on the road ahead of you that you completely fail to notice a car swerve into your lane of traffic.

Because your attention is directed elsewhere, you aren’t able to react in time, potentially leading to a car accident. Experiencing inattentional blindness has its obvious consequences (as illustrated by this example), but, like all biases, it is not impossible to overcome.


There are many theories that seek to explain why we experience this form of cognitive bias. In reality, it is probably some combination of these explanations.

Conspicuity holds that certain sensory stimuli (such as bright colors) and cognitive stimuli (such as something familiar) are more likely to be processed, and so stimuli that don’t fit into one of these two categories might be missed.

The mental workload theory describes how when we focus a lot of our brain’s mental energy on one stimulus, we are using up our cognitive resources and won’t be able to process another stimulus simultaneously.

Similarly, some psychologists explain how we attend to different stimuli with varying levels of attentional capacity, and this might affect our ability to process multiple stimuli at once.

In other words, an experienced driver might be able to see that car swerve into the lane because they are using fewer mental resources to drive, whereas a beginner driver might be using more resources to focus on the road ahead and unable to process that car swerving in.

A final explanation argues that because our attentional and processing resources are limited, our brain dedicates them to what fits into our schemas or our cognitive representations of the world (Cherry, 2020).

Thus, when an unexpected stimulus comes into our line of sight, we might not be able to process it on the conscious level. The following example illustrates how this might happen.


The most famous study to demonstrate the inattentional blindness phenomenon is the invisible gorilla study (Most et al., 2001). This experiment asked participants to watch a video of two separate groups passing a basketball and to count how many times the white team passed the ball.

Participants are able to accurately report the number of passes, but what they fail to notice is a gorilla walking directly through the middle of the circle.

Because this would not be expected, and because our brain is using up its resources to count the number of passes, we completely fail to process something right before our eyes.

A real-world example of inattentional blindness occurred in 1995 when Boston police officer Kenny Conley was chasing a suspect and ran by a group of officers who were mistakenly holding down an undercover cop.

Conley was convicted of perjury and obstruction of justice because he supposedly saw the fight between the undercover cop and the other officers and lied about it to protect the officers, but he stood by his word that he really hadn’t seen it (due to inattentional blindness) and was ultimately exonerated (Pickel, 2015).

The key to overcoming inattentional blindness is two maximize the attention you do have by avoiding distractions such as checking your phone. And it is also important to pay attention to what other people might not notice (if you are that driver, don’t always assume that others can see you).

By working on expanding your attention and minimizing unnecessary distractions that will use up your mental resources, you can work towards overcoming this bias.

Preventing Cognitive Bias

As we know, recognizing these biases is the first step to overcoming them. But there are other small strategies we can follow in order to train our unconscious mind to think in different ways.

From strengthening our memory and minimizing distractions to slowing down our decision-making and improving our reasoning skills, we can work towards overcoming these cognitive biases.

An individual can evaluate his or her own thought process, also known as metacognition (“thinking about thinking”), which provides an opportunity to combat bias (Flavell, 1979).

This multifactorial process involves (Croskerry, 2003):

(a) acknowledging the limitations of memory,

(b) seeking perspective while making decisions,

(c) being able to self-critique, and

(d) choosing strategies to prevent cognitive error.

Many of the strategies used to avoid bias that we describe are also known as cognitive forcing strategies, which are mental tools used to force unbiased decision-making.


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Saul Mcleod, PhD

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Educator, Researcher

Saul Mcleod, Ph.D., is a qualified psychology teacher with over 18 years experience of working in further and higher education.

Charlotte Ruhl

Marketing Associate Analyst

B.A., Psychology, Harvard University

Charlotte Ruhl is a recent Harvard College graduate with more than six years of research experience in clinical and social psychology.