Superiority bias
One of the first studies that found the effect of illusory superiority was carried out in 1976 by the College Board in the USA. A survey was attached to the SAT exams (taken by approximately one million students per year), asking the students to rate themselves relative to the median of the sample (rather than the average peer) on a number of vague positive characteristics. In ratings of leadership ability, 70% of the students put themselves above the median.  In ability to get on well with others, 85% put themselves above the median, and 25% rated themselves in the top 1%.