Composite image containing a drawing of a check mark, a drawing of a teacup with a sale price, and a drawing of news coverage of a shark attack

Common cognitive biases


Humans, like other life forms, are the result of millions of years of evolution. For the most part, evolution has set us up for success in the world today. Our brains and behaviors have been shaped to help us survive, even thrive.

But what used to be advantageous for us in the past is not always advantageous to us today; unfortunately, our brains don’t seem to have caught up to this idea yet!

Here’s an example: our ancestors lived in close-knit bands of people. We protected ourselves from marauders by learning to be suspicious of people who are not like us, those people not from our tribe.

But we no longer live in tiny groups of similar humans, and, even if we do, so many of us are professionally and socially connected to hundreds, even thousands of people all over the world. The original strategy of “run from difference” needed to shift when we realized the value of interacting with others quite different from us.

As the key point of Darwin’s Origin of Species is sometimes paraphrased, “It is not the strongest who will survive, nor the most intelligent, but the ones who are most adaptive to change.”

Discover some of the common cognitive mistakes our brains have evolved to make in the modules below. Ask yourself how they may play a role in your own actions and the potential costs from them you may needlessly bear. Learn what you might do about them.

No matter our personality or profession, we can all agree that it’s smart to attend to the progress of science and become aware of the quirks of human cognition.

  1. A yellow checkmark

    “The DNA is a Match”: Confirmation Bias


    We have more information at our fingertips than ever before… but this doesn’t mean we’re making better decisions. From DNA analysis to political debates to fantasy football, our desire to confirm our beliefs skews how we interpret the data in front of us.

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    Are you making the best choices for your Fantasy Football league? Learn more about “The mistake almost everyone makes in fantasy football” (and how to avoid it) at ESPN.

    Have you ever taken a personality test such as the Myers-Briggs Type Indicator? You answer a list of questions, and in the end you get four letters that seem to describe you to a “T”. Here’s the problem: these letters apply to lots of people. But like weekly astrological predictions, when we read these general descriptions confirming our own personality or experiences, we don’t realize that they would seem equally real to everybody. And as we keep reading, we keep confirming – ignoring imprecisions and delighting in the accuracies. Personality tests are fine when they’re just a fun activity, but we can run into issues when we use them as a hiring and promotion tool. Read more at the New York Times.

    The sequence 2, 4, 8 follows a rule. Can you figure out what it is? Try to outsmart the confirmation bias with this demo from the New York Times.

    “Imagine a business considering launching a new product. The CEO has an idea for the ‘next big thing’ so he directs his team to conduct market research to explore its feasibility. The team then carries out surveys, focus groups, and competitive analyses with this in mind.” Can you see the confirmation bias at work? Here’s three tips on how to avoid it from Patrick Healy and the Harvard Business Review.

    “We all have a few people in our social media networks who share ridiculous things [… b]ut most of us have also encountered well-informed, sane people who share articles that are blatantly incorrect propaganda. Why does this happen?” Read more in Jeff Stibel’s “Fake news: How our brains lead us into echo chambers that promote racism and sexism” (USA Today).

    Warren Buffett is one the most successful investors in history. His secret? He “acknowledges that even his decisions could be swayed by [confirmation bias] – an important first step – and then gives voice to opinions that contradict his own.” Read more about how to think (and invest) like Buffet from Forbes.

    “It’s easy to assume that presenting factual information will automatically change people’s minds, but messages can have complex, frustrating persuasive effects […] It turned out that climate change skeptics – whether politically conservative or liberal – showed more resistance to the stories that mentioned climate change. Climate change themes also made skeptics more likely to downplay the severity of the disasters. At the same time, the same articles made people who accept climate change perceive the hazards as more severe.” Read more from Professor Ryan Weber’s “Extreme weather news may not change climate change skeptics’ minds” at The Conversation.

  2. What Sentence Would You Give?:
    Watch for the Anchoring Bias


    We’ve all heard of cases where two people receive very different sentences for committing identical crimes. One hidden bias that can influence these kinds of decisions is the Anchoring Effect.

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    Should your social security number influence how much you’d pay for a bottle of wine? Of course not! But behavioral economist Dan Ariely shows otherwise in a study where he auctioned off everyday items to students. Watch Dan’s explanation of the study here to learn how the anchoring bias can influence consumer decisions.

    Often, the anchoring effect is discussed in the context of numbers: in our video, we saw how judges’ sentencing decisions could be influenced by even random numbers (like a roll of the dice). But we can anchor on ideas too. The podcast DDx explores what this can mean for doctors in their episode “Anchoring bias and the frequent flyer” featuring Dr. Gita Pensa.

  3. Drawing of woman presenting the breaking news of a shark attack

    The Availability Bias


    What’s more likely: death by shark attack, or death by lightning strike? Most people choose the wrong answer. Why? It's the availability bias—our tendency to assume that events that come easily to mind must be more common or true.

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    Test yourself. Try the demo.

    The San Francisco Police Department will now limit their release of mug shots to cases that require public assistance or public warning. Why this shift? Every person who is arrested has their photo taken during the booking process. When released, these photos often remain in the public domain… even when charges are dropped or the individual is found not guilty. This can lead to a type of availability bias called an illusory correlation: “When two rare things occur simultaneously [like crime and, by definition, minority status], our minds tend to overestimate the relationship between those two things,” says Berkeley professor Jack Glaser. When we see these mug shots, “the distinctiveness of blackness and crime going together stands out [and] is more likely to be remembered”. Our minds then believe this relationship is more true, which can lead to dangerous errors in judgment from how we perceive innocent actions (like checking out of an Airbnb) to who we stop and search and even how we speak to each other.

    Vaccines have eradicated diseases. No scientific data shows a connection between vaccination and autism. So why is fear of autism motivating some parents’ decisions not to vaccinate their children? Read Sarah Watt’s article “5 cognitive biases that explain why people still don’t vaccinate” at Forbes.

    “If you’re not using a formal, methodical system to make product decisions, measure your sales pipeline, track your VC meetings, evaluate your marketing efforts, etc., you’re doing something seriously wrong.” Why? The availability bias. For more, read Dan Schipper’s article “We all have a bias that makes it hard to know if we’re successful” at Quartz.

    There’s a common belief that women in their 30s stop working in order to start families. However, a global survey by the ICEDR found that men and women around 30 were leaving work at the same rates, and for the same reasons: to work for a competitor. Read more here.

    Dr. Harrison Alter suspected pneumonia when Blanche Begaye arrived at the emergency room with breathing trouble even though tests didn’t reveal the typical symptoms. It wasn’t until Begaye was admitted that Alter realized his mistake: she was suffering from aspirin toxicity, not pneumonia at all! The culprit behind his mistake? Availability bias. Alter had seen dozens of people in the past few weeks suffering from pneumonia, and this influenced his diagnosis despite the lack of proof in Begaye. Learn about how availability bias and other heuristics can impact a doctor’s decisions at The New Yorker.

    Want more examples of the Availability Bias in action? Business Insider sifts truth from availability here (featuring Professor Adam Grant).

  4. Drawing of a teacup and saucer with a card showing regular price and sale price.

    The Endowment Effect


    We overvalue the things we own. This is fine when it’s a family keepsake or memento – but how does this influence the decisions we make about homes, investments, and more?

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    Want to learn more about Dr. Anagol’s research on the endowment effect? See The Economist’s “To have and to hold: The endowment effect among stockmarket investors”.

    We see evidence of endowment effects for lottery tickets, coffee mugs, even the letters of our own name. But new research conducted at Vanderbilt shows humans’ “greater tendency to overvalue things that are related to survival and reproduction”. In the study, items rated as more likely to “directly help its owner survive and thrive” (like a pill for maintaining perfect weight or a luxury car) produced the greatest endowment effects. The trend towards overvaluing items more strongly related to health and status “may reflect the potential evolutionary origins of the effect”. What’s more, this tendency, and the endowment effect broadly, isn’t limited to humans! Researchers found the same effects in chimps and orangutans. Read more at

    This Washington Post article looks at how return policies take advantage of the endowment effect to influence shoppers’ decisions.

    “Both the Boston Red Sox and the Chicago White Sox had rather mediocre seasons last year. The Red Sox have some exciting young hitters but a lack of decent pitchers. The White Sox have almost the exact opposite problem … So the argument was to put a Chicago White Sox’ message board: would they trade their great young pitcher Chris Sale for two excellent and even younger hitters from the Red Sox, Xander Bogaerts and Mookie Betts?” From John Auther’s 2015 Financial Times article: “Investors psyched by the endowment effect”.

    For a broader introduction to how we think, and where our blindspots are, check out Daniel Kahneman’s NYT Bestseller and Winner of the National Academy of Sciences Best Book Award (2012): Thinking, Fast and Slow.