The United States will conduct its 22nd population census in 2000 -- a record of taking a census every ten years since 1790. The U.S. Constitution requires that a decennial census be taken for reapportionment of seats in the U.S. House of Representatives. In practice, the census also provides the information needed for congressional districts to be drawn for the 435 House members. Background From the beginning, the U.S. census has added information about the population beyond the absolute minimum required for reapportionment and redistricting. The 1790 census asked households about each member's age, sex and family relationship. The 1820 census added questions about nativity and industry; subsequent censuses added questions about occupation, military service, income, education and other important information. Census results, therefore, are not only fundamental for congressional apportionment and redistricting but also for providing information to organizations and people who make decisions about many issues. These include matters of public relevance such as health and education, transportation planning and community services, and private concerns -- such as siting of businesses, housing, consumer marketing and economic strategies. This article presents an overview of the historical basis for the United States' decennial census, the importance of census results, and the complex problems and issues associated with taking a modern census. Purpose of the U.S. Census The fundamental and original purpose of the census in the United States was to provide data for reapportionment of the U.S. House of Representatives. Article I of the U.S. Constitution mandates that an enumeration shall be made of the population every ten years. Since the 1930 census, the 435 seats of the U.S. House of Representatives have been automatically reapportioned upon delivery of the population counts from the Bureau of the Census. Once the Secretary of Commerce transmits the decennial census count for each of the states to the president, the reapportionment of the Congress is determined quickly. The U.S. Constitution specifies that the number of congressional seats is to be apportioned to each state according to its population. Once congressional seats are assigned to each state, the geographic boundaries for each district must be redefined. The Congress requires the Census Bureau to provide decennial census population tabulations to state officials for legislative reapportionment and redistricting within one year after the April 1 census date. The Tabulation Process The census begins with construction of a nationwide address register that incorporates elaborate procedures to ensure that the coverage and tabulation will be as complete as possible. Every residential address receives census forms, with instructions on return mailing of the completed questionnaire. Traditionally, not all households return their completed forms within a reasonable period of time. As a result, a large staff of census enumerators are in place to visit those households that do not respond to the main questions regarding the number of family members and their key demographic characteristics. Through this intensive follow-up effort, census officers determine whether a particular unit -- house or apartment -- is occupied and obtain the answers to the key questions. The process also incorporates special programs to reach specific groups (such as homeless people; those in institutions, dormitories or barracks; others who do not reside in standard households). The results from the returned mail questionnaires, enumerator follow-ups and intensive special coverage improvement efforts -- when combined -- produce the final census count of the U.S. population. The Data The mail questionnaire that most households in the 2000 census will receive is a "short form" that asks a limited number of questions about household members. Historically, the census has collected additional content beyond this minimal query on age, sex and race that is needed from all households for the constitutional purposes of reapportionment and redistricting. Since 1960, most of the additional data have been collected on a separate sample form (also known as the "long form") sent to a fraction of households. These added details are widely used to serve many important public purposes. The census short form sent to all households will include seven questions -- six related to population characteristics and one related to housing. The longer form will incorporate the questions on the short form and pose a total of 52 queries. Historically, the decennial census has included questions on race and ethnicity, although the specific questions asked have often changed. These changes have occurred because of shifts in the racial and ethnic makeup of the population, changes in social attitudes and political concerns and the evolving needs of the U.S. Government for racial statistics. The increased racial and ethnic diversity, changing attitudes about race and ethnicity and increased use of census data have added attention and controversy over census questions on race and ethnicity. The 1990 census included a race question that asked each person to identify himself or herself as Caucasian, black or Negro, American Indian, Eskimo, Aleut, Asian or Pacific Islander, or other. American Indians were asked to provide a specific tribal affiliation. Asian or Pacific Islanders were asked to select from a list of nationality groups. Separate from the race question, respondents were asked if they were of Spanish or Hispanic origin or descent and, if so, to choose Mexican, Puerto Rican, Cuban or other. The 2000 census will include race and Hispanic items similar to 1990, but respondents will have the opportunity to check more than one race group. Unlike previous censuses, in which persons of multiple racial backgrounds were compelled to check "other" and then write in a response, the 2000 census will collect direct information on the specific backgrounds for persons of multiple racial ancestry. The Census Undercount: A Growing Challenge Although the census count of the U.S. population has never been complete, public concerns about the incompleteness have increased in recent decades -- particularly because the census is the sole basis for apportionment of congressional seats and relied on heavily for the distribution of U.S. Government funds. Improved statistical and demographic techniques now enable the Census Bureau to estimate the incompleteness of the census with a greater accuracy than in the past. Some undercount of the population occurs in the censuses of all countries. In the United States, demographic analysis of coverage shows that the net undercount here (the number of people omitted from the U.S. census minus the number overcounted) was estimated at 7.0 million in 1940, 6.3 million in 1950, 5.6 million in 1960, 5.5 million in 1970, 2.8 million in 1980, and 4.7 million in 1990. In percentage terms, the undercount rate for the population dropped steadily from 1940 (5.4 percent) to 1980 (1.2), before rising in 1990 (1.8). According to the 1990 estimates by demographic analysis, almost three-fourths of the net national undercount consisted of nonblacks (primarily whites). The rate of undercount, however, was over four times higher for blacks than for nonblacks, 5.7 percent and 1.3 percent, respectively. Special 1990 decennial census surveys revealed that net undercount rates were also higher for other racial and ethnic minorities. The undercount of Asian and Hispanic groups was likely to have been influenced by the relatively large numbers of foreign-born persons. Immigrants may not have understood census questionnaires and procedures. There is widespread agreement among stakeholders and politicians about several changes that the Census Bureau has proposed for the 2000 census. Census questionnaires will be simpler and clearer. For example, there will be more use of color to highlight where respondents will provide the information sought. Moreover, new partnerships will be formed with local city, county and state officials. There will be a "complete count" committee formed in every state to work with the Census Bureau, to ensure that all state agencies are cognizant of what a complete census count entails. In addition, the U.S. Bureau of the Census will spend $100 million on paid advertising to help promote participation in the forthcoming tabulation. An intriguing partnership is being formed with the nation's students and educators. The Census Bureau is distributing copies of a free curriculum, "Making Sense of Census 2000," to tens of thousands of public and private elementary and secondary schools across the United States. The purpose is to encourage families, through the students in the household, to respond to the request for census information. A heightened targeting will take place in areas with traditionally low census-response rates. Realistically, the Census Bureau cannot succeed in its efforts without widespread support and participation by the U.S. populace. Partnerships with state and local governments will be needed in the campaign. One special goal for improved cooperation between the Census Bureau and local governments is to reach agreement on the nationwide address register for the decennial census, since approximately one-half of the census undercount is attributable to missed housing units. The new methods promise to reduce the amount of missing data, thus reducing the census undercount. Ultimate Uses of Census Data The census is unique among statistical programs of the U.S. Government because it is reasonably accurate even for small geographic areas and small population subgroups. The government also collects information using administrative records and surveys, but the census alone provides a broad range of information encompassing the entire population that can be cross-tabulated for those smaller geographic and population units. Federal, state and local governments, plus such private sector elements as the academic and business communities, use census data extensively. Indeed, since the availability of computer-readable data files beginning with the 1970 census, there has been an explosion in the use of census data by a wide range of users for a variety of purposes. Within the U.S. statistical framework, the census serves important functions. They include: providing estimates for program management and government reports (e.g., the Immigration and Naturalization Service relies on census information on the foreign-born for its reports that are ordered by Congress); denominators for vital statistics (e.g., birth and death rates) used, for instance, by public health officials to monitor the health conditions of the U.S. population; and information to update age, sex and race data for the ongoing weighting of household sample surveys -- in other words, to reflect as accurately as possible the current distribution of the population. As for state and local governments, they use this information to identify those in need of particular services, and to allocate facilities and resources to serve people most effectively. Census statistics are crucial to the private sector as well. Business organizations, universities and other research arms, the nonprofit world, the media, academia and individual citizens find data vital, often when combined with data from their own research. Corporations make important decisions on marketing and sales based on population statistics. Research organizations use census data to advance knowledge that may frequently have policy implications, such as to track educational advancement to calculate better the degree of need for adult literacy programs. And the media use these statistics for purposes of informing the public on myriad matters -- for instance, population changes and the extent to which that change depends on migration. Ultimately, the United States could not function properly and effectively without the decennial census. This has been true for the past two centuries, and it will, no doubt, be equally true in the coming millennium. ---------- Barry Edmonston is director of the Center for Population Research and Census at Portland State University (Oregon). He is author of a recent study on the census, The 200 Census Challenge, for the Population Research Bureau in Washington, D.C.