But again isn't the fact that, "perceptions of ability were positively related to actual ability, although in this case, not to a significant degree" an interesting result? Not the fact that they were related, but the fact that they mostly weren't! That does demonstrate the core result as I understand it, that people are little better than random at evaluating their own performance, which was a surprising finding.
Nope, because I think D-K played a neat little trick. Whether it was intentional or not is another topic. They were using a largely homogenous group of people - Cornell undergrads taking psychology classes, and querying them on things where all performance would fall close to a similar mean.
Imagine you take 100 literal clones of somebody and query them on something, and then ask them to predict their performance. Assuming these clones are smart, they'd all estimate their performance as being at 50%, which is what would be expected. But due to natural variance, not everybody will score identically (in the same way even identical twins do not perform identically). And so you'd end up seeing some huge D-K effect with literal clones! Those at the bottom would be greatly overestimating their performance, while those at the top would be greatly underestimating it. Now step away from clones into the regular world of students, where everybody is going to think they're a bit better than average, and you get people predicting a score of about 60%. Now suddenly you see the same thing, except the lower performers would be overestimating their performance by a greater degree than the top performers were underestimating theirs.
To truly measure D-K, you'd need an extremely heterogenous group of people, and you'd also need questions with perceived and real domain expertise. Would a farmer with a 5th grade education evaluate his performance on a differential equations test as above average? Would a professor of diff eq evaluate his performance on a test of optimal growth strategies for buckwheat and corn, as above-average? Of course not, but then you can't make a shocking claim, don't get published, and don't become famous.
