Dunning-Kruger Effect

A type of cognitive bias where people fail to adequately assess their level of competence or incompetence. Individuals of low ability experience illusory superiority (i.e., an overestimation of one's own qualities and abilities in relation to the same qualities and abilities of others) and incorrectly assess their cognition at a level greater than it is. In other words, individuals of low ability, without metacognition, cannot accurately evaluate their level of ability. Conversely, people of high ability incorrectly assume that tasks that appear trivial to them are trivial for everyone. Moreover, competent individuals tend to underestimate their abilities compared to others and experience impostor syndrome (i.e., a psychological pattern in which an individual doubts their accomplishments and has a persistent fear as being exposed as a “fraud”).

It is important to point out that this bias applies to everyone, not just individuals of high or low ability, but to anyone who may fall somewhere in between as well (note the continuity of the graph below). Further, an individual who may find themselves learned in one area, while being weak in another will experience different aspects of this bias (i.e., overconfidence in one area and underestimation of one's abilities in another). In other words, it is important to weigh the affect of this bias on an individual's knowledge within each domain of knowledge versus in general.


1) Recently, Julie has become very interested in the topic of vaccine safety and the possibility of a vaccine-autism link (in reality, no such link exists [1]). Her whole endeavor in this area began when she came across a documentary series called “The Truth about Vaccines.” Within, she found herself being persuaded by “experts” that there was a very serious problem with vaccine safety that the public wasn't being told about. In other words, she was convinced of a conspiracy between the scientists and governments of the world to hide the truth about vaccine safety. After watching the series, she then went on to learn more about the “dangers of vaccines” through YouTube videos and other various anti-vaccine websites.

As a result of her newly acquired knowledge, Julie has decided to start a Facebook group on the “dangers of vaccines” in order to educate the public about this conspiracy. Within, she touts much of the same anti-vaccine nonsense that she has learned and even refers to herself as an “expert” on the topic.

*Note, Vaccines, like any medical intervention available, are not free from risk. In fact, within the scientific community, we refer to them as “unavoidably unsafe” as is the case with all efficacious medical interventions on the market today. However, just because a medicine carries a small risk, doesn't mean that it should be avoided as it is important to weigh the risks and benefits appropriately. In the case of vaccines, the reward is very high (i.e., prevention of a serious diseases such as polio) while the risk is very small. We know this from decades of scientific inquiry that have produced thousands of studies on this topic [2].

Explanation: Julie, is NOT an expert and for her to believe otherwise is quite foolish. While she has put a great deal of effort into attempting to inform herself about vaccines, the hours of “research” that she has conducted is NOT tantamount to the training that medical doctors or scientists receive. Furthermore, the vast majority of her information sources are not credible and she has chosen to read only into one side of the story (i.e., the anti-vaccine narrative).

In this case, Julie is unaware of how much she doesn't know and is falling into the illusory superiority trap. In other words, Julie, in terms of her knowledge regarding vaccines, is a low-ability individual who is incorrectly assessing her cognition on this subject at a level much higher than it really is.

2) Stan was recently accepted to MIT for engineering as he was top of his class in high school along with many other accolades. These achievements coupled with both a high ACT and SAT score was enough for his acceptance into the University. His first semester on campus, he decided to take a normal load of courses and still found himself struggling badly. While he certainly wasn't alone in his struggles, he couldn't believe that this was happening to him as he has always achieved at a high level academically. Due to his recent poor performance, Stan begins to question whether or not he deserves to be there. He begins to have a persistent belief that maybe MIT was wrong about him and that he's not worthy of attending such a prestigious institution.

Explanation: Stan is definitely experiencing impostor syndrome here. Yes, he may be struggling with his courses, but so do many students their first semester in college, regardless of what institution they are attending as the transition between high school and college courses can be overwhelming.

3) One of Donald Trump's campaign promises was that he was going to repeal and replace the Affordable Care Act (ACA) with a better plan that would be “a lot less expensive” and “take care of everyone” [3].

After he became President, Donald Trump did go to work to try and fulfill his campaign promise of repealing and replacing the ACA. Yet, he was not able to successful complete this task as he didn't have a full understanding of the complexities of healthcare. In fact, after he became apprised to the complications surrounding healthcare on a national level, Trump implicitly admitted to his naivety by saying “Nobody knew healthcare could be this complicated” [4]. The reality is that most knew how complicated healthcare was in this country, while Trump did not until he tried to change it.

Explanation: Trump was a victim of the Dunning-Kruger effect here. He drastically overestimated his ability in healthcare policy as he wrongly assumed that it was a subject that lacked complexity. Bluntly, Trump was ignorant to a degree that he was unaware of how much he didn't know.

*Note, this assumes that Trump was genuinely telling the American public the truth throughout his campaign on this topic. There's a possibility that he was deliberately inflating his rhetoric surrounding healthcare in order to convince his audience despite the fact that he actually knew how complicated healthcare is and that he wouldn't be able to fulfill this promise completely. In my opinion, there's a very high probability (i.e., >80%) that this is actually the case as most politicians lie, to a degree, throughout their campaigns. That said, Trump is an outlier when it comes to lying as he appears to do it regularly. According to Politifact, Trump only tells the truth or makes “mostly true” statements 16% of the time where he is outright lying 47% of the time [5].

How to Minimize this Bias

Unfortunately, cognitive biases can never be completely eliminated, but they can be minimized. For this particular bias, it is important to stop and try to gain a more holistic perspective of the situation. That is, you're going to want to seek out as much information as possible about the particular topic of concern in an attempt to understand the bigger picture.

What is more, it is important to seek out the science if it exists and seek out multiple, credible scientific authority figures who are informed about this particular topic. These scientific authority figures act as a conduit for the information coming from the community and will be able to tell you the conclusion(s) reached from all of the scientific evidence gathered to date on the topic. Instead of relying on first impressions or doing what your “gut” is telling you, it is important to take these steps before making any decisions.

Now, let's re-evaluate the three scenarios above for the steps that each individual should have taken in order to minimize the effects of this bias.

1) Julie should have sought more information regarding the benefits of vaccines instead of solely concentrating on safety issues. Further, instead of listening to anti-vaccine “experts,” she should have searched for actual experts in medical science to hear their thoughts on the benefits of vaccines and their possible side effects (i.e., safety concerns). Last, there is a plethora of science available on this topic that has routinely shown that the benefits far outweigh the risks [6].

2) Stan should have taken a moment to reflect on all of his accomplishments to date and reminded himself that MIT only admits high-achieving individuals. While he may be struggling, it is important to put this into perspective and remind himself that he is struggling in courses taught at the best engineering school in the world. He has every right to be there and, if he works hard enough, will get through this obstacle and graduate.

3) Assuming that Trump wasn't deliberately lying to his constituents during his campaign, he should have taken the time to speak with healthcare experts to properly understand the complexities surrounding it. If he had done this, he would have been better positioned throughout his campaign to accurately convey the state of healthcare to his audience and how he could realistically fix it for them once in office. However, given that Trump abhors experts, scenarios of this nature (i.e., Trump speaking about issues that he has a cursory understanding of as if he is as learned as an expert) continue to happen in other areas beyond healthcare and will most likely continue given current trends.


Cognitive biases are a constant threat to critical thinking as they are, unfortunately, always present due to our inherently flawed minds. That said, there is still room for hope, as we've discussed here, once you have learned about the particular cognitive bias, there are steps that can be taken to minimize it. Moreover, as we've discussed previously, a cognitive bias is not the same as a logical fallacy.

If you find yourself being influenced by this cognitive bias, it doesn't automatically mean that the argument you subsequently construct will be bad. This does mean, however, that there is a strong possibility that the argument is not the best argument. As a Critical Thinker, you should take a moment to re-evaluate the situation/topic after you've thoroughly conducted a holistic investigation. Only then can you be confident that the Dunning-Kruger effect isn't leading you down an irrational path.


[1] Taylor, Luke E., Swerdfeger, Amy L., Eslick, Guy D, Vaccines are not associated with autism: An evidence-based meta-analysis of case-control and cohort studies. Vaccine (2014) Volume 32, Issue 29.

[2] CDC, Vaccine Safety Publications.

[3] Jackson, Henry C. 6 Promises Trump has made about health care. Politico (2017).

[4] Hellman, Jessie. Trump: 'Nobody knew that healthcare could be so complicated'. The Hill (2017).

[5] Donald Trump's File. Politifact.

[6] Vaccine Benefits. National Institute of Allergy and Infectious Diseases.