The Rise of the Bipolar Neighborhood

Problem: Although planners aim to provide for income diversity in the communities they serve, too little is known about how income distributions in metropolitan neighborhoods are changing. Purpose: We investigate whether neighborhood income diversity has increased since 1970 by examining neighborhoods in the 100 largest U.S. metropolitan areas. Methods: We analyze neighborhoods in the 100 largest U.S. metropolitan areas from 1970 to 2000 using a combination of nominal (H) and ordinal (E) entropy indices. We focus on neighborhoods we call bipolar, (where E/H > 1), in which very low- and very high-income groups predominate. We investigate these with tract-level statistics and by using a counterfactual. Results and conclusions: We find a dramatic increase in the number and incidence of these bipolars since 1970. Compared to other neighborhoods, we find that, on average, bipolars have significantly greater shares of very high-income families, racial diversity, shares of middle-aged persons, and shares of renters. We use a counterfactual to reveal that much of the growth in bipolars over the last three decades has been fueled by income distributions at the metropolitan scale becoming more bimodal, with fewer middle-income families. Gentrification appears to explain only a minor share of growth in bipolars. Takeaway for practice: Metropolitan census tracts with pronounced bimodal income distributions have become more common since 1970. This appears to reflect changing metropolitan income distributions more than spatial rearrangement, although planning policies may be responsible in some instances. Whether residence in bipolar. neighborhoods will benefit very low-income households by reducing stereotyping and expanding social opportunities is unclear, but such places should be monitored.