> There's also: If you take 1 class in piano 30 years ago and can only play 1 simple song, that might put you in the 90th percentile worldwide just because most

> There's also: If you take 1 class in piano 30 years ago and can only play 1 simple song, that might put you in the 90th percentile worldwide just because most people can't play at all. But you might be at the 10th percentile amongst people who've taken at least 1 class. So doing a global ranking can be very difficult if you aren't exactly sure what the denominator set looks like. Yes, and this literally implies that people in the lowest quartiles can't and won't rate themselves to be in the lowest quartiles when they are forced to give an answer. (Especially on tests that doesn't measure anything (getting jokes? really?), on tests that they have no knowledge about (how would they know that how their classmates perform on an IQ test???), or on tests that just have a high variance.) And therefore they will "overestimate their performance". It's like grouping a bunch of random people, and forcing them to answer whether their house is short, average or high. The "people living in short houses" will "overestimate the height of their houses", while the "people living in towers" will humbly say they live in an average high house. Is this an existing and relevant psychological phenomenon, different from the general inability to guess unknown things? I don't think so. If you think so, then give me proof.