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In this article, the authors use a special data set compiled for 60 U.S. metropolitan areas to examine 1970-1980 trends in the distribution of family income and shifts in the degree of segregation between income groups. They document how these changes contributed to increases in the spatial concentration of affluence and poverty during the 1970s and estimate simple descriptive models that connect these outcomes to broader socioeconomic trends in U.S. urban areas.

This article develops and applies two expressions for the rate of change of a population's mean age. In one, aging is shown to be negatively related to contemporary birth rates and death rates. In a general sense, aging occurs when vital rates are too low, as illustrated through applications to the United States, the Netherlands, and Japan. The other expression relates the rate of aging to a population's demographic history, in particular to changes in mortality, migration, and the annual number of births. Applications to the United States and Sweden show that the dominant factor in current aging in these countries is a history of declining mortality. Migration also contributes significantly but in opposite directions in the two countries. The two approaches are integrated after recognizing that the rate of change in the mean age is equal to the covariance between age and age-specific growth rates. A decomposition of this covariance shows that the two seemingly unrelated expressions contain exactly the same information about the age pattern of growth rates.