I think a lot of it is class dynamics, as well as geography. Detroit is very spread out and most white collar workers who work in the city live in the suburbs -

I think a lot of it is class dynamics, as well as geography. Detroit is very spread out and most white collar workers who work in the city live in the suburbs - Royal Oak, Bloomfield, Clarkston, etc. The areas being gentrified by young professionals that would be considered "Detroit" are concentrated in the Downtown and Midtown districts. Hamtramck is in the gentrification process as well, but it's considered a separate city. Basically the fact that the newly-relocated white collar workers are all spread out and are offset by the mostly blue-collar old guard likely explains why it wouldn't make the top of the "Brain concentration" index. Ann Arbor, on the other hand, makes more sense because its geography is so much more centralized, and is only supported by a few bedroom communities (Dexter, Selene, and Chelsea)