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 The Census Bureau has used a variety of statistical groupings of counties to present data in recent decades. Its most significant nationwide set of county combination schemes consisted of the State economic areas (SEAs) and economic subregions (ESRs) first defined for the 1950 census. The SEA/ESR framework provided a sub-State counterpart of regions and divisions; both groupings, the one using States and the other using counties, covered the entire United States. They both served as sets of general-purpose summary units in the Census Bureau’s statistical presentations for several censuses.

The SEAs and ESRs were the product of a special study that the Census Bureau sponsored in cooperation with the Bureau of Agricultural Economics, U.S. Department of Agriculture, and several State and private agencies. The statistical criteria looked for homogeneity of socioeconomic characteristics, industry, land use, and agriculture. In terms of size, each SEA had to contain at least 100,000 people and use counties as the building blocks. Each SEA usually consisted of several counties that, with certain rare exceptions, had to be contiguous. Moreover, within a State, the geographic pattern of the SEAs was designed to facilitate further combination across State lines into ESRs. The SEAs also took into account the framework of metropolitan areas that appeared for the first time in the 1950 census publications. Where a metropolitan area extended across a State line, the segment within each State comprised a single SEA.

The SEAs and ESRs appeared in several publications of the 1950 decennial census. The Census Bureau continued to use the SEA/ESR system, with minor changes, in its publications of the 1960 and 1970 decennial censuses. The boundaries and the component units of SEAs remained largely unchanged following their initial establishment. In the 1950 census, the Census Bureau reported data for 501 SEAs; in the 1960 census, for 509; and, in the 1970 and 1980 censuses, 510. The Census Bureau discontinued the tabulation and publication of summary data by SEAs Statistical Groupings6-21