^ Raleigh-Durham-Chapel Hill isn’t a city, but it is a MSA which appears to be the principal unit the authors used. I think the point is that it’s not the sheer number or concentration of MDs and JDs, but the average level of educational attainment. Parts of the Research Triangle are still part of the old industrial South, especially Durham which apart from Duke is basically a beat-up old industrial town with large numbers of less educated blue collar workers and retirees from those jobs. That brings down the average.