What Is a Cognitive Bias? Meaning, Examples and How to Check Yours

Everyone has a few thinking habits that reliably lead them astray. You hold on to a failing project because of what you have already put in. You judge a price as fair because of the first number you heard. You notice the news that agrees with you and skim past the rest. These are cognitive biases.

This guide explains what the term means, where biases come from, the ones that matter most in everyday life, and what the research says about catching them, including the awkward finding that being clever does not protect you as much as you might hope.

What a cognitive bias means

A cognitive bias is a systematic error in judgment: a gap between how people actually reason and how a careful, logical answer would come out, which shows up in the same direction again and again. The word "systematic" is what separates a bias from an ordinary mistake. Random errors scatter. Biases lean one way, so they can be predicted.

The modern study of biases began with Amos Tversky and Daniel Kahneman's 1974 paper in Science. They argued that people judge uncertain things using a few mental shortcuts, called heuristics, which are usually helpful but produce predictable errors in some situations. Their three original heuristics were:

• Availability: judging how common something is by how easily examples come to mind.
• Representativeness: judging probability by how much something resembles a typical case, while ignoring base rates.
• Anchoring and adjustment: starting from a number you were given and adjusting too little away from it.

Bias, heuristic, fallacy, distortion

These words get mixed up. A heuristic is the shortcut itself, and it is often useful. A bias is the predictable error a shortcut produces in the wrong setting. A logical fallacy is a flaw in the structure of an argument, so it is about how you argue rather than how you judge. A cognitive distortion is a term from cognitive behavioral therapy for exaggerated thought patterns, such as catastrophizing, that feed anxiety or low mood.

Fast and slow thinking

The most popular way to explain biases is the dual-process framework, made famous by Kahneman's book Thinking, Fast and Slow. It describes two kinds of thinking:

• Fast (often called System 1 or Type 1): automatic, quick and effortless. It reads faces, finishes familiar sentences and gives you a gut answer.
• Slow (System 2 or Type 2): deliberate, effortful and limited by working memory. It does long division and checks whether the gut answer holds up.

Biases tend to appear when a fast, intuitive answer is accepted without the slow check. Jonathan Evans and Keith Stanovich, two of the leading researchers on dual-process theories, caution that "two systems" is a simplification. It is better to think of two kinds of process than two separate parts of the brain. As a practical model, though, it is useful: most debiasing advice is a way of making the slow check happen at the right moment.

Shortcuts exist for good reasons. They are fast and cheap, and in familiar settings they are often right. The trouble comes in unfamiliar, high-stakes or statistical decisions, where the shortcut's answer feels just as convincing as it does when it is correct.

The major biases, with checks you can use

A few classic findings behind the table. In Tversky and Kahneman's anchoring experiment, people saw a random number from a rigged wheel of fortune before estimating the share of African countries in the United Nations, and their estimates moved toward that meaningless number. Prospect theory, from Kahneman and Tversky's 1979 paper, formalized the finding that losses loom larger than gains. Arkes and Blumer showed in 1985 that people who had paid more for a season ticket attended more plays, even though the money was already gone. Baruch Fischhoff found in 1975 that once people knew how events turned out, they overestimated how likely they would have judged that outcome beforehand.

The bias blind spot

Learning about biases has an odd side effect: you start seeing them everywhere, mostly in other people.

Emily Pronin, Daniel Lin and Lee Ross named this the bias blind spot in 2002. Across three studies, people rated themselves as less susceptible to a list of biases than the average person, even after the biases were described to them. The reason is partly how we judge. We judge others by their behavior, but ourselves by our intentions and introspection, and introspection cannot see biases because they work below awareness.

Does intelligence protect you?

Less than you would think. Keith Stanovich and Richard West ran seven studies in 2008 and found that many classic biases, including anchoring, framing effects, base-rate neglect, myside bias and the sunk cost effect, were largely unrelated to cognitive ability. Higher ability did help with a few others, such as belief bias in logic problems and some probability tasks.

The bias blind spot is even less forgiving. In 2012, West, Meserve and Stanovich found that cognitive ability did not reduce the blind spot at all. If anything, people with higher ability showed a slightly larger one.

The likely reason is that intelligence measures how well you can reason once you start, not whether you notice that a situation calls for careful reasoning. Stanovich calls the second part rational thinking disposition: the habit of questioning your first answer. That habit can be practiced. If you are interested in the reasoning side, our IQ test uses visual puzzles where the first answer that looks right is often a trap, which is a small version of the same skill.

Can you reduce bias? What works

For a long time, the honest answer was "not much". Early debiasing training had weak results, so researchers focused on changing incentives and how choices are presented. More recent work is more encouraging.

• One-off training can help. In two experiments, Carey Morewedge and colleagues (2015) found that a single session, either an interactive game or an instructional video, produced medium to large reductions in several biases. The effects were still there two months later, and games with personalized feedback worked better than videos.
• It can carry into real decisions. Sellier, Scopelliti and Morewedge (2019) gave 290 graduate students in professional programs the training and, separately and without warning, a business case modeled on the decision to launch the Space Shuttle Challenger. Trained students were 19% less likely to choose the inferior, hypothesis-confirming answer.
• Consider the opposite. Lord, Lepper and Preston (1984) found that asking people to imagine how they would judge evidence if it had pointed the other way reduced biased judgments more than simply telling them to be fair.
• Run a premortem. Gary Klein's premortem asks a team to imagine the project has failed and write down why. It turns the hunt for confirming evidence into a hunt for weak points.

A short checklist for big decisions

1. Slow down. If it is not an emergency, sleep on it. Urgency favors the fast answer.
2. Set your own anchor. Write your estimate before you see anyone else's.
3. Find the base rate. How often does this kind of plan, investment or project usually succeed?
4. Argue the other side. State the strongest case against your choice in a way its supporters would accept.
5. Ignore sunk costs. Ask only: given where I am now, what is the best next step?
6. Judge the process, not the outcome. Good decisions can turn out badly through luck, and bad ones can turn out well.

For related reading, see our explainers on the sunk cost fallacy and survivorship bias.

Questions people ask

What is a cognitive bias in simple terms?

It is a predictable mistake in judgment caused by a mental shortcut. The shortcut usually works, but in some situations it pushes your conclusions in the same wrong direction every time.

What are the most common cognitive biases?

Confirmation bias, anchoring, the availability heuristic, loss aversion, the sunk cost fallacy and hindsight bias are among the best studied and the most common in daily decisions.

Are cognitive biases ever useful?

The shortcuts behind them are useful most of the time. They let you decide quickly with little effort, and in familiar situations they are often right. The bias is the cost of using a good shortcut in the wrong place.

Can smart people avoid cognitive biases?

Not reliably. Research by Stanovich and West found many biases were largely unrelated to cognitive ability, and higher ability did not shrink the bias blind spot. Habits of checking your own thinking matter more.

Can you get rid of cognitive biases completely?

No. But training, checklists and techniques like considering the opposite can reduce their effect, especially on decisions where you deliberately stop to use them.