The Changing Incidence and Severity of Poverty Spells among Female-Headed Families by David Card and Rebecca M. Blank. Published in volume 98, issue 2, pages 387-91 of American Economic Review, May 2008

Schelling (“Dynamic Models of Segregation,” Journal of Mathematical Sociology 1 (1971), 143–186) showed that extreme segregation can arise from social interactions in white preferences: once the minority share in a neighborhood exceeds a “tipping point,” all the whites leave. We use regression discontinuity methods and Census tract data from 1970 through 2000 to test for discontinuities in the dynamics of neighborhood racial composition. We find strong evidence that white population flows exhibit tipping-like behavior in most cities, with a distribution of tipping points ranging from 5% to 20% minority share. Tipping is prevalent both in the suburbs and near existing minority enclaves. In contrast to white population flows, there is little evidence of nonlinearities in rents or housing prices around the tipping point. Tipping points are higher in cities where whites have more tolerant racial attitudes.

The onset of Medicare eligibility at age 65 leads to sharp changes in the health insurance coverage of the U.S. population. These changes lead to increases in the use of medical services, with a pattern of gains across socioeconomic groups that varies by type of service. While routine doctor visits increase more for groups that previously lacked insurance, hospital admissions for relatively expensive procedures like bypass surgery and joint replacement increase more for previously insured groups that are more likely to have supplementary coverage after 65, reflecting the relative generosity of their combined insurance package under Medicare.