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Residential housing patterns (also known as residential segregation) usually describe the distribution of different groups across units within a larger area. To examine the residential housing patterns of racial and ethnic groups, an appropriate area and its component parts or units of analysis must be chosen. The unit of analysis - the smaller geographic area - presents alternatives. While census tracts are the most common choice, blocks or block groups could also be used. The technical paper The Effects of Using Census Block Groups Instead of Census Tracts When Examining Residential Housing Patterns (PDF -- 154k) discusses the effect of using a smaller unit of analysis—the census block group in comparison to census tracts.
We have computed indexes for Metropolitan Areas (as defined on June 30, 1999) at the block group and census tract level. Indexes for Metropolitan/Micropolitan Areas (as defined on June 6, 2003) and places are computed at the census tract level only.
Block groups are clusters of census blocks created by the Census Bureau as a geographic level between blocks and census tracts to permit the release of tabulated data that cannot be presented at the block level for confidentiality purposes. Block groups generally contain between 600 and 3,000 people. Block groups never cross the boundaries of states or counties; census tracts consist of one or more block groups.
Census tracts, which typically have between 1,500 and 8,000 people, with an average size of about 4,000 people, are defined with local input, are intended to represent neighborhoods (they are designed to be relatively homogeneous with respect to population characteristics, economic status, and living conditions). They typically do not change much from census to census, except to subdivide due to population growth or to combine as a result of substantial population decline. The Census 2000 was the first decennial census in which the entire United States was covered by census tracts. Census tracts are often chosen by other researchers in their analysis of residential housing patterns.
Geography Glossary (PDF -- 420k) for
more information on the definition of block groups, census tracts, places and/or MSA/PMSAs). Or get more information on Metropolitan and Micropolitan Statistical Areas
(as defined on June 6, 2003).
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