Leniency bias

In the field of social psychology, illusory superiority is a condition of cognitive bias whereby a person overestimates that person's own qualities and abilities, in relation to the same qualities and abilities of other persons. Illusory superiority is one of many positive illusions, relating to the self, that are evident in the study of intelligence, the effective performance of tasks and tests, and the possession of desirable personal characteristics and personality traits.

The term illusory superiority first was used by the researchers Van Yperen and Buunk, in 1991. The condition is also known as the Above-average effect, the superiority bias, the leniency error, the sense of relative superiority, the primus inter pares effect, and the Lake Wobegon effect.

Illusory superiority has been found in individuals' comparisons of themselves with others in a variety of aspects of life, including performance in academic circumstances (such as class performance, exams and overall intelligence), in working environments (for example in job performance), and in social settings (for example in estimating one's popularity, or the extent to which one possesses desirable personality traits, such as honesty or confidence), and in everyday abilities requiring particular skill.

For illusory superiority to be demonstrated by social comparison, two logical hurdles have to be overcome. One is the ambiguity of the word "average". It is logically possible for nearly all of the set to be above the mean if the distribution of abilities is highly skewed. For example, the mean number of legs per human being is slightly lower than two because some people have fewer than two and almost none have more. Hence experiments usually compare subjects to the median of the peer group, since by definition it is impossible for a majority to exceed the median.

A further problem in inferring inconsistency is that subjects might interpret the question in different ways, so it is logically possible that a majority of them are, for example, more generous than the rest of the group each on "their own understanding" of generosity. This interpretation is confirmed by experiments which varied the amount of interpretive freedom. As subjects evaluated themselves on a specific, well-defined attribute, illusory superiority remains.

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