"Although the wealthiest Americans have always lived in their own islands of privilege, sociologists and demographers say the degree to which today’s professional class resides in a world apart is a departure from earlier generations. People of widely different incomes and professions commonly lived close enough that they mingled at stores, sports arenas and school. In an era in which women had fewer educational and professional opportunities, lawyers married secretaries and doctors married nurses. Now, lawyers and doctors marry each other.
A recent analysis of census data by sociologists Sean Reardon of Stanford and Kendra Bischoff of Cornell highlighted how middle-income neighborhoods have been fading away as more people live in areas that are either poor or affluent."