Dunning-Kruger effect, inpsychology, acognitivebias whereby people with limited knowledge or competence in a givenintellectual or social domain greatly overestimate their own knowledge or competence in that domain relative to objectivecriteria or to the performance of their peers or of people in general. According to the researchers for whom it is named, psychologistsDavid Dunning andJustin Kruger, the effect is explained by the fact that themetacognitive ability to recognize deficiencies in one’s own knowledge or competence requires that one possess at least a minimum level of the same kind of knowledge or competence, which those who exhibit the effect have not attained. Because they are unaware of their deficiencies, such people generally assume that they are not deficient, in keeping with the tendency of most people to “choose what they think is the most reasonable and optimal option.” Although not scientifically explored until the late 20th century, the phenomenon is familiar from ordinary life, and it has long beenattested in common sayings—e.g., “A little knowledge is a dangerous thing”—and in observations by writers and wits through the ages—e.g., “Ignorance more frequently begets confidence than does knowledge” (Charles Darwin).

In the studies reported on in their paper “Unskilled and Unaware of It: How Difficulties in Recognizing One’s Own Incompetence Lead to Inflated Self-Assessments” (1999), Dunning and Kruger tested the abilities of four groups of young adults in three domains:humour,logic (reasoning), andgrammar. The results supported their predictions that, as compared with their more competent peers, “incompetent individuals…will dramatically overestimate their ability and performance relative to objective criteria”; that they “will be less able…to recognize competence when they see it” (whether their own or someone else’s); that they “will be less able…to gain insight into their true level of performance” by comparing their own performance with that of others; and, paradoxically, that they can improve their ability to recognize their own incompetence by becoming more competent, “thus providing them[selves] the metacognitive skills necessary to be able to realize that they have performed poorly.”

Dunning and Kruger emphasized that the effect they had identified does not imply that people always overestimate their own knowledge or competence. Whether they do so depends in part on the domain in which they evaluate themselves (most golfers do not believe that they are better at golf thanTiger Woods) and whether they possess “a minimalthreshold of knowledge, theory, or experience” that, given the effect, would lead them to the false belief that they are knowledgeable or competent. Nor does the effect imply that motivational biases and other factors do not also play a role in producing inflated self-assessments among incompetent people.

Later investigations of the Dunning-Kruger effect explored its influence in a variety of other domains, including business, medicine, and politics. For example, a study published in 2018 indicated that Americans who know relatively little about politics and government are more likely than other Americans to overestimate their knowledge of those topics. Moreover, according to the study, that tendency seems to be more pronounced in partisancontexts in which people consciously think of themselves as supporters of one or the other (Republican orDemocratic) majorpolitical party.