Census Bureau

Population Estimates: Concepts

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What is a population estimate?

The Census Bureau's Population Estimates Program (PEP) produces estimates for years since the last decennial census (1990), as well as past decades. Existing data series such as births, deaths, Federal tax returns, medicare enrollment, and immigration, are used to update the decennial census counts. PEP estimates are used in Federal funding allocations, in setting the levels of national surveys, and in monitoring recent demographic changes. A methodology reference accompanies most of our population estimates offerings.
How are estimates different from projections?
There is not a distinct dichotomy between population estimates and population projections, but there are some general differences. Estimates are for the past, while projections typically are for future dates. Estimates generally use existing symptomatic data collected from various sources, while projections must assume what demographic trends will be in the future. At the Census Bureau, the population projections use the latest available estimates as starting points. In our current product offerings the user may see both an estimate and a projection available for the same reference date (e.g., July 1993), which may not agree because they were produced at different times. In such cases, estimates are the preferred data.
Revisions to estimates and detail.
With each new issue of July 1 estimates, PEP revises estimates for years back to the last census. Previously released estimates become superseded. Revisions to estimates are usually due to revisions to input data, or changes in methodology.

The frequency of estimates, and the level of demographic detail available from PEP varies by geographic level.

Why does the Census Bureau produce estimates?
The legal requirement for the Census Bureau to produce subnational population estimates is given in Title 13 of the U.S. Code. Title 13 states that:

"During the intervals between each census of population required under section 141 of this title, the Secretary, to the extent feasible, shall annually produce and publish for each State, county, and local unit of general purpose government of fifty thousand or more, current data on total population and population characteristics and, to the extent feasible, shall biennially produce and publish for units of general purpose government current data on total population."

The reason for producing estimates is given in Section 183 of Title 13:

"Except as provided in subsection (b), for the purpose of administering any law of the United States in which population or other population characteristics are used to determine the amount of benefit received by State, county, or local units of general purpose government, the Secretary shall transmit to the President for use by the appropriate departments and agencies of the executive branch the data most recently produced and published under this title."

In other words, the Census Bureau produces subnational estimates for use in the allocation of funds to state, county and local governments. Because these population estimates are used for fund allocation by governments, PEP estimates populations for those areas which have functioning governments. Functioning governments are those that have elected officials who can provide services and raise revenue, while nonfunctioning governmental entities exist primarily for administrative purposes. In addition to states and counties, these areas include incorporated places and minor civil divisions, which serve as functioning government units.

For what geographic areas does the Census Bureau produce estimates?
In addition to the Nation and the 50 states, PEP produces estimates for the following geographic entities:

Counties:
Counties are the primary legal divisions of most states. In Louisiana, these primary divisions are known as parishes. In Alaska, the county equivalents, beginning with the 1980 census, consist of 1) the organized boroughs and 2) the "census areas" delineated for statistical purposes by the State of Alaska and the Census Bureau. In four states (Maryland, Missouri, Nevada, and Virginia), one or more cities are independent of any county organization and thus constitute primary divisions of their states; the Census Bureau refers to these places as "independent cities" and PEP treats them as the equivalents of counties for estimates purposes. A portion of Yellowstone National Park in Montana also is treated as a county equivalent. The District of Columbia has no primary divisions and the entire area is considered to be the equivalent of a county for estimates purposes.

Each state and statistically equivalent entity is covered in its entirety by counties or statistically equivalent entities. Most, but not all, counties are functioning governmental units, whose powers and functions vary from state to state. Except for the establishment of two new counties (one each in Arizona and New Mexico) and several changes in the boroughs and census areas of Alaska, there were no significant changes in the county structure between 1980 and 1990. Since 1990, the boroughs of Denali and Yakutat have been added in Alaska, and the independent city of South Boston, Virginia has merged with Halifax County.

Minor Civil Divisions (MCDs):
Legally defined county subdivisions are referred to as minor civil divisions. They comprise both governmentally functioning entities -- that is, those that have elected officials who can provide services and raise revenues -- and nonfunctioning entities that exist primarily for administrative purposes. Twenty-eight states and all the territories have MCDs, although the MCDs are functioning governmental units in all or part of only 20 states. PEP produces estimates for all MCDs that are governmentally functioning entities and for nonfunctioning MCDs in counties that contain at least one functioning MCD.

The legal powers and functions of MCDs vary from state to state. Many of the MCDs in 12 states (Connecticut, Maine, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Wisconsin) serve as full, general-purpose local governments, and the Census Bureau presents the same array of decennial census data for these MCDs that it provides for places.

MCDs primarily are called towns (in New England, New York, and Wisconsin), townships, and districts, but also include a variety of other entities. In Maine and New York, American Indian reservations are not part of any other MCD and therefore, the Census Bureau treats them as MCDs. PEP does not produce separate estimates for American Indian Reservations regardless of their MCD status. In some states, all or some incorporated places are subordinate to the MCDs in which they are located. Therefore, a place may be either independent of or dependent upon MCDs. In one state (Ohio), a multi-county place may be treated differently from county to county. The District of Columbia defined no MCDs for the 1990 census, so the District itself serves as the equivalent of an MCD for data presentation purposes.

Incorporated Places:
The legal designations, powers, and functions of incorporated places vary from state to state. Incorporated places include cities, towns (except in New England, New York, and Wisconsin where the Census Bureau recognizes towns as MCDs for census purposes), boroughs (except in Alaska, where the Census Bureau recognizes boroughs as equivalents of counties, and New York, where the Census Bureau recognizes the five boroughs that constitute New York City as MCDs) and villages. PEP produces estimates for all incorporated places. Incorporated places can cross both county and MCD boundaries. When an incorporated place is in more than one county or MCD, the place name is followed by the designation "pt." (which stands for part) in PEP tabulations. Because counties are not entirely composed of incorporated places, PEP produces "balance of county" estimates. The county balance is the county population minus the county population residing in incorporated places.

Consolidated Cities:
Consolidated cities represent a special type of governmental unit that the Census Bureau recognized specifically for the first time in the 1990 decennial and 1992 economic censuses. A consolidated government is a unit of local government for which the functions of an incorporated place and its county or MCD have merged. Where one or more other incorporated places within the consolidated government continue to function as separate governmental units, the primary incorporated place is referred to as a consolidated city.

In PEP tabulations, estimates are not shown for consolidated cities. Instead estimates are shown for the consolidated city "remainder," which is the consolidated city minus the semi-independent places located within the consolidated city. In 1994, PEP displayed estimates for six places -- Butte-Silver Bow, MT; Columbus, GA; Indianapolis, IN; Jacksonville, FL; Milford, CT; and Nashville-Davidson, TN -- as remainders.

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Source: U.S. Census Bureau, Population Division,
Population Distribution Branch

Maintained By: Laura K. Yax (Population Division)
Last Revised: March 26, 1999 at 01:03:59 PM

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