Depicted below is the general relationship between the way we actually perform and the way we predict we will perform:
It looks to me like this is a copy of the graph summarizing the results of one of the four studies (specifically, the third) in the cited paper. It is not accurate to describe it as “the general relationship”. The other three studies don’t show the same curve, although they all do show the bottom quartile predicting their ability as above the median but below the top quartile.
One thing I’ve always found suspicious about this paper: Why report quartiles? The four studies had n=65, 45, 84, 140 respectively. Why choose to bin this large number of participants into only four bins? That seems unusually low resolution. Why quartiles and not quintiles or deciles?
You’re exactly right, sorry. I’ll keep the picture because I think it suffices to illustrate the trend, but I’ll update my description for clarity. Here are the other summary graphs for studies 1, 2, and 4
It looks to me like this is a copy of the graph summarizing the results of one of the four studies (specifically, the third) in the cited paper. It is not accurate to describe it as “the general relationship”. The other three studies don’t show the same curve, although they all do show the bottom quartile predicting their ability as above the median but below the top quartile.
One thing I’ve always found suspicious about this paper: Why report quartiles? The four studies had n=65, 45, 84, 140 respectively. Why choose to bin this large number of participants into only four bins? That seems unusually low resolution. Why quartiles and not quintiles or deciles?
You’re exactly right, sorry. I’ll keep the picture because I think it suffices to illustrate the trend, but I’ll update my description for clarity. Here are the other summary graphs for studies 1, 2, and 4
ETA: Strangely apropos this post, David Dunning is doing a Reddit AMA right now; I should go ask him why he and Kruger (1999) chose to report quartiles!