The Dunning–Kruger effect is a cognitive bias whereby people with low ability at a task overestimate their ability. Some researchers also include in their definition the opposite effect for high performers: their tendency to underestimate their skills. The Dunning–Kruger effect is usually measured by comparing self-assessment with objective performance. For example, the participants in a study may be asked to complete a quiz and then estimate how well they did. This subjective assessment is then compared with how well they actually did. This can happen either in relative or in absolute terms, i.e., in comparison with one's peer group as the percentage of peers outperformed or in comparison with objective standards as the number of questions answered correctly. The Dunning–Kruger effect appears in both cases but is more pronounced in relative terms: the bottom quartile of performers tend to see themselves as being part of the top two quartiles. The initial study was published by David Dunning and Justin Kruger in 1999. It focuses on logical reasoning, grammar, and social skills. Since then, various other studies have been conducted across a wide range of tasks. These include skills from fields such as business, politics, medicine, driving, aviation, spatial memory, exams in school, and literacy.