Berry, Christopher R., and Edward L. Glaeser. "Divergence of Human Capital Levels across Cities." KSG Faculty Research Working Paper Series RWP05-057, October 2005 (also NBER Working Paper 11617).
Over the past 30 years, the share of adult populations with college degrees increased more in cities with higher initial schooling levels than in initially less educated places. This tendency appears to be driven by shifts in labor demand as there is an increasing wage premium for skilled people working in skilled cities. In this paper, we present a model where the clustering of skilled people in metropolitan areas is driven by the tendency of skilled entrepreneurs to innovate in ways that employ other skilled people and by the elasticity of housing supply.