The story below was first published on Oct. 16 by the Cornell Chronicle, which is produced by the communications office at Cornell University.

Since 1970, middle‐income neighborhoods have been disappearing. In 2009, only 42 percent of families lived in middle‐income neighborhoods, compared with 65 percent four decades earlier, reports a new Cornell-Stanford study. More than one-third of families now live in either affluent or poor neighborhoods, double the proportion in 1970.

The study, authored by Kendra Bischoff, assistant professor of sociology at Cornell, and Sean Reardon, professor of education at Stanford, is the result of analyzing 40 years of census data. It was just released by the U.S. 2010 Project, a program of research on changes in American society in the recent past.

Increasing income inequality is one of the primary reasons for the growth of income segregation.

“As income inequality has grown in the last four decades, America has become increasingly spatially divided by income,” said Bischoff. “This trend has been more rapid in the last decade, but the direction of change has been evident for many years.”

The researchers also found that high‐income families – the top 10 percent of earners in each metropolitan area – are more segregated from the rest of the population than are families in the bottom 10 percent.

“In 2010 the 10 percent of families with the highest incomes controlled approximately 46 percent of all income in the United States,” write Bischoff and Reardon, noting that “the increasing isolation of the affluent from low‐ and moderate‐income families means that a significant proportion of society’s resources are concentrated in a smaller and smaller proportion of neighborhoods.”

The report analyzes changes in segregation in the 117 largest metropolitan areas in the United States. The analyses indicate some of the causes of increasing income segregation:

• Most (70 percent) of the increase in segregation – and especially the increase in segregation of wealthy families – is due to increasing income inequality.
• Class segregation has grown more in areas with a growing percentage of children in the population. Where people are more concerned about opportunities for their children, there may be more incentive for affluent families to cluster in separate neighborhoods.
• Income segregation has risen particularly rapidly in areas where the manufacturing sector has declined. This is likely because manufacturing declines have reduced the middle class population in cities.

The authors warn that the increasing isolation of the rich can affect other groups by reducing the shared stake in public resources and amenities that can benefit broad segments of the population, such as schools, parks and public services.

“If advantaged families do not share social environments and public institutions with low‐income families, they may be less likely to support investment in these shared resources. Such a shift in collective commitment to the public good may have far‐reaching consequences for social inequality,” said Reardon.

“Income segregation” refers to the extent to which high‐ and low‐income families within a metropolitan area live in the same neighborhoods.

An earlier version of this research, conducted while Bischoff was at Stanford, was made public a couple of years ago, as detailed in a release from the study's sponsors. Bischoff was a postdoctoral fellow at Stanford received her PhD in sociology from Stanford, where Reardon was one of her advisors. Reardon is a member of Stanford's Center for Educational Policy Analysis, a hub for economic and sociological research and data analysis involving many faculty members and graduate students from the Stanford Graduate School of Education.

U.S. 2010 Project is funded by the Russell Sage Foundation and Brown University.

In other research, Reardon and colleagues have documented resegregration in public schools (see news release).

Reardon also wrote a commentary earlier this year in the Sunday Review section of The New York Times detailing how the growing income gap has contributed to a widening of the achievement gap.