You nailed it. This would be a good title: "It's better to be un-cool, finds study by former un-cool children." I'm pretty sure there's no accepted definition

You nailed it. This would be a good title: "It's better to be un-cool, finds study by former un-cool children." I'm pretty sure there's no accepted definition of cool. They seem to have chosen early signs of delinquency as their definition. If you pried, you could probably find out the names of the children from these researchers' own pasts who the study participants were based on.