Their analysis suggests that their data is pretty well-explained by a combination of a “Closer-To-The-Average Effect” (which may or may not be rational — there are multiple possible rational reasons for it) and a “Better-Than-Average Effect” that appear ~uniformly across the board (but getting swamped by the “closer-to-the-average effect” at the upper end).
Here’s the best explanation + study I’ve seen of Dunning-Krueger-ish graphs: https://www.clearerthinking.org/post/is-the-dunning-kruger-effect-real-or-are-unskilled-people-more-rational-than-it-seems
Their analysis suggests that their data is pretty well-explained by a combination of a “Closer-To-The-Average Effect” (which may or may not be rational — there are multiple possible rational reasons for it) and a “Better-Than-Average Effect” that appear ~uniformly across the board (but getting swamped by the “closer-to-the-average effect” at the upper end).