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 Central Region as Midwest, the Census Bureau continued the same system of geographic units for the 1990 census publications.

Several Census Bureau publications use the regions and divisions to summarize data tabulations from the decennial censuses. Among these, the most important reports constitute chapters of major subject-matter fields that summarize population and housing characteristics. These reports present summaries of both complete-count and sample data from the census of population and housing for the Nation as a whole, as well as data for the regions, divisions, States, urban and rural areas, the metropolitan and nonmetropolitan categories, and the other basic geographic units. In addition, various presentations from the other censuses and sample surveys use regions and divisions as part of their geographic summary units.

Although the system of regions and divisions has remained largely unchanged for many decades, the data user community periodically suggests new approaches to large-area summary geography. The Census Bureau, in turn, examines these proposals and considers them as possible improvements to the existing framework of State groupings.

One major review took place after the 1950 census, when an interagency committee within the Department of Commerce compared the existing Census Bureau regions and divisions to other schemes of regionalization and assessed the usefulness of an alternative system. Because the existing State groupings resulted largely from tradition, with few major changes from the 1880 set of summary units, it seemed worthwhile to test these combinations by using more modern statistical approaches and techniques. The following ground rules guided the study:
 * Socioeconomic homogeneity is the principal criterion for grouping States into regions.
 * Each combination should consist of two or more adjacent States. 6-18Statistical Groupings