What Is… the Dunning-Kruger Effect

The Dunning-Kruger effect: a cognitive bias

In this series, I dig a little deeper into the meaning of psychology-related terms. This week’s term is the Dunning-Kruger effect.

The Dunning-Kruger effect was first described by psychologists David Dunning and Justin Kruger. It’s a type of cognitive bias that causes people to feel confident that they have greater knowledge or competence in an area than they actually do. Dunning and Kruger’s research was partly inspired by Charles Darwin’s observation that “ignorance more frequently begets confidence than does knowledge.”

Another influence in their research was McArthur Wheeler; in 1995, he robbed two banks in broad daylight with no attempt at disguise. He was later surprised when police arrested him, as he thought that applying lemon juice to his face had made him invisible to security cameras. Despite being as dumb as a sack of potatoes, he was sufficiently confident that he thought he could get away with two bank robberies.

When does the Dunning-Kruger effect appear?

This cognitive bias comes into play when people have insufficient knowledge to recognize that there’s a whole schwack of stuff they don’t know they don’t know. Because of that basic lack of awareness, or metacognition, people may not be able to recognize the distinction between themselves and people who do actually have knowledge/capability.

The effect has been demonstrated across multiple different areas of knowledge. It’s most often seen in people who know the least. In particular, it’s mostly observed in the bottom quartile (bottom 25% of performers in a given testing group). In some cases, study participants whose scores on knowledge tests were in the bottom 10% of the participant group estimated that they’d done better than about 70% of the group. Essentially, people who completely bombed the test thought that their performance was above average.

Susceptibility to the Dunning-Kruger effect doesn’t happen across the board. In Dunning and Kruger’s tests, the top 25% of performers actually showed the opposite pattern; they were actually more likely to underestimate their relative performance. The driving factor for this appeared to be that high scorers assumed that if they’d performed well, their peers must have done well also, shifting the grading curve.

The problem with surface knowledge

Considering the diagram below, usually, when you start to learn things in any sort of depth, that brings a corresponding expansion of the area in quadrant III (what you know you don’t know). You don’t actually possess that knowledge yet, but you know it’s there.

modified Johari window of knowledge: from what you know to what you don't know you don't know

The Dunning-Kruger effect shows up when people don’t have enough knowledge in quadrant I to develop a corresponding awareness of a lack of knowledge in quadrant III, and quadrant IV (what’s entirely unknown) isn’t even on the radar.

So, watching ER gives you some surface knowledge of medicine and medical jargon, but if you haven’t managed to pick up some awareness of what you don’t know, you may think you’re ready to start doing random medical procedures on some poor, unsuspecting victim.

A similar bias is the above average effect. Consistently, more than 50% of people in a group believe they’re above average, which just isn’t possible.

What about Trump?

A Washington Post article offered Donald Trump as a prime example of the Dunning-Kruger effect in action. I’m inclined to think the same; whether you like him or not politically, he talks big talk about things that he obviously doesn’t know anything about.

His sparring with Dr. Fauci seems like a good example of Dunning and Kruger’s finding that people experiencing this cognitive bias aren’t able to recognize the distinction between themselves and people who actually are knowledgeable/capable. It doesn’t exactly set a good example to the bottom 25% who are likely to overestimate their own knowledge.

Have you noticed any examples of the Dunning-Kruger effect in action?


The Psychology Corner: Insights into psychology and psychological tests

The Psychology Corner has an overview of terms covered in the What Is… series, along with a collection of scientifically validated psychological tests.

Ashley L. Peterson headshot

Ashley L. Peterson


Ashley is a former mental health nurse and pharmacist and the author of four books.

28 thoughts on “What Is… the Dunning-Kruger Effect”

  1. I did know about the opposite, or rather, the Hartford effect, ie. the factt that if you know some fact, you’re inclined to think everyone does. I had also heard of the above average effect, but had never heard of the Dunning-Kruger effect.

    1. I did not know about the Hartford Effect. I was going to post that I wish there were an effect that was the opposite of the Dunning-Kruger Effect, and there you have it.

      I very often make the mistake of assuming that someone is aware of something that I am, and the danger in doing so has sometimes led to misapplications of both Hanlon’s and Occam’s Razors (which Ashley discussed in a previous post.)

      For example, once somebody described what was clearly an upper-middle class background, and then closed their description with the statement: “So you might say we were lower middle class.”

      Hanlon’s Razor states: “Never attribute to malice that which can be explained by ignorance.”
      But because I couldn’t believe that anyone would be so ignorant as not to know the true definition of “lower middle class,” my mind generated all kinds of reasons why they would have said such a thing — all of them malicious in nature.

      Occam’s Razor states: “All other things being equal, the simplest explanation is always the best.” All of the explanations that supported the idea that this person was malicious were very complicated in nature. That they simply had lived such a sheltered life as to never have been made aware of class distinctions, and that they simply did not know the definition of “lower middle class,” was a much simpler explanation. But my mind rejected the simple truth because I couldn’t believe that anyone could be so ignorant.

      Thanks for sharing about the Hartford Effect. I’ll look into it now more deeply.

      1. I think something like socioeconomic class depends to a large extent on one’s frame of reference. If one is exposed mostly to people of a higher socioeconomic class, they’re probably more likely to round down when it comes to their own, regardless of where they fall in absolute terms.

        I was looking up the Hartford effect, and it’s a specific example of the bias more broadly known as the curse of knowledge; it people know that Hartford is the capital of Connecticut, they’re likely to overestimate other people’s knowledge of that particular fact.

        1. I don’t the meaning of the expression “round down” and was unable to completely understand your first paragraph.

          I haven’t yet explored the Hartford Effect but I take it Hartford is the capital of Connecticut. I thought it was interesting how if I had applied either Hanlon’s or Occam’s Razor to the person’s naive statement, I’d have been more likely to have seen the truth sooner. I’m certain he was not malicious, but that certainty didn’t arise until quite a lot of unneeded mental turmoil, trying to figure it.

            1. Well, yes he was. He was somebody who through a combination of having been born into extreme privilege and being an incredibly hard worker — one might say, “workaholic” — he managed to do quite well for himself, probably beyond millionaire. Unfortunately, he felt that this entitled him to lecture people on how they could do better themselves, and I was not the only person who decided to shun his company.

  2. The thing about Dr Fauci though, since my husband is a PhD medicinal chemist with 30 years in the field, is his political points before scientific fact. And his ever changing policies to side with one-sided politics. His newest blunder? Open schools and shut down bars. His no mask/mask might have scientific basis. But our masks are not efficiently protecting us. Just enough to allow us to grocery shop or fill corporate coffers but not small businesses.

    1. As an educator, I appreciate this comment (Based in knowledge!) more than I can truly express.

      I resigned earlier this year, after it was apparent that federal and state funding trumped (Quite literally, that bozo!) the health and welfare of BOTH district employees and the children (and families) of our community.

      It’s been a long, hard year of misinformation, and the sad realization that so few of us matter to those in power.

        1. I try to be optimistic, just because reality is so dark. I feel powerless, but do what I can to add a little glitter to my insignificant little corner of this brutally polarized landscape.

  3. Wow. This explains so much that my head just went “Pop!” and all the air leaked out with a slow, high-pitched squeal. Holy crap… 😧

  4. Yes, in particular I had an incompetent co-worker in the mid-90s for a year or two, which was maddening, as he wore a tie every day, and this seemed to be what mattered to management!

  5. I already commented in depth, because I was exuberant upon learning of the Hartford Effect. But to answer Ashley’s question, I think that same person was a very good example of the Dunning Kruger effect. He was forever lecturing me on various topics as though he knew more than I did, but he was not intelligent enough to realize that I knew more on those topics than he did.

    (Evidently, he was also lacked the savvy to realize that people in general don’t like to receive huge loads of unsolicited advice.)

  6. Oh yeah, McArthur Wheeler & the all-powerful lemon juice! I forgot about that.

    I think the politicians would make a good case study for this effect.

    Fortunately I don’t think I’m too prone to this effect as I just assume I’m thick as shit & don’t know anywhere near enough about anything. Then it’s a nice surprise if it turns out I’m smarterer than I thought 😉

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