This section presents statistics on the growth, distribution, and characteristics of the U.S. population. The principal source of these data is the U.S. Census Bureau, which conducts a decennial census of population, a monthly population survey, a program of population estimates and projections, and a number of other periodic surveys relating to population characteristics. For a list of relevant publications, see the Guide to Sources of Statistics in Appendix I.

Decennial censuses-The U.S. Constitution provides for a census of the population every 10 years, primarily to establish a basis for apportionment of members ofthe House of Representatives among the states. For over a century after the first census in 1790, the census organization was a temporary one, created only for each decennial census. In 1902, the Census Bureau was established as a permanent federal agency, responsible for enumerating the population and also for compiling statistics on other population and housing characteristics.

Historically, the enumeration of the population has been a complete count. That is, an attempt is made to account for every person, for each person’s residence, and for other characteristics (sex, age, family relationships, etc.). Since the 1940 census, in addition to the complete count information, some data have been obtained from representative samples of the population. In the 1990 and 2000 censuses, variable sampling rates were employed. For most of the country, 1 in every 6 households (about 17 percent) received the long form or sample questionnaire; in governmental units estimated to have fewer than 2,500 inhabitants, every other household (50 percent) received the sample questionnaire to enhance the reliability of sample data for small areas. Exact agreement is not to be expected between sample data and the 100-percent count. Sample data may be used with confidence where large numbers are involved and assumed to indicate trends and relationships where small numbers are involved.

Census Bureau data presented here have not been adjusted for underenumeration. Results from the evaluation program for the 1990 census indicate that the overall national undercount was between 1 and 2 percent. The estimate from the Post Enumeration Survey (PES) was 1.6 percent, and the estimate from Demographic Analysis (DA) was 1.8 percent. Both the PES and DA estimates show disproportionately high undercounts for some demographic groups. For example, the PES estimates of percent net undercount for Blacks (4.4 percent), Hispanics (5.0 percent), and American Indians (4.5 percent) were higher than the estimated undercount of non-Hispanic Whites (0.7 percent). Historical DA estimates demonstrate that the overall undercount rate in the census has declined significantly over the past 50 years (from an estimated 5.4 percent in 1940 to 1.8 percent in 1990), yet the undercount of Blacks has remained disproportionately high.

Current Population Survey (CPS)-Thisis a monthly nationwide survey of a scientifically selected sample representing the noninstitutional civilian population. The sample is located in 754 areas with coverage in every state and the District of Columbia and is subject to sampling error. At the present time, about 60,000 occupied households are eligible for interview every month; of these about 7.5 percent are, for various reasons, unavailable for interview.

While the primary purpose of the CPS is to obtain monthly statistics on the labor force, it also serves as a vehicle for inquiries on other subjects. Using CPS data, the Bureau issues a series of publications under the general title of Current Population Reports, which cover population characteristics (P20), consumer income (P60), special studies (P23), and other topics.

Estimates of population characteristics based on the CPS will not agree with the counts from the census because the CPS and the census use different procedures for collecting and processing the data for racial groups, the Hispanic population, and other topics. Caution should also be used when comparing estimates for various years because of the periodic introduction of changes into the CPS. Beginning in January 1994, a number of changes were introduced into the CPS that effect all data comparisons with prior years. These changes include the results of a major redesign of the survey questionnaire and collection methodology and the introduction of 1990 census population controls, adjusted for the estimated undercount. This change in population controls had relatively little impact on derived measures such as means, medians, and percent distribution, but did have a significant impact on levels.

Population estimates and projections -National population estimates start with decennial census data as benchmarks and add annual population component of change data. Component of change data come from various agencies, as follows: National Center for Health Statistics (births and deaths), Immigration and Naturalization Service (legal immigrants), Office of Refugee Resettlement (refugees), U.S. Census Bureau’s International Programs Center (net movement between Puerto Rico and the U.S. mainland), Armed Forces, Department of Defense, and Office of Personnel Management (movement of military and civilian citizens abroad). Emigration and net undocumented immigration are projected based on research using census data. Estimates for states, counties, and smaller areas are based on the same component of change data and sources as the national estimates. School statistics from state departments of education and parochial school systems, federal income tax returns from the Internal Revenue Service, group quarters from the Federal-State Cooperative program and the Veterans Administration, and medicare data from the Centers for Medicare and Medicaid Services are also included.

Data for the population by age for April 1, 1990 (shown in Table 12) are modified counts. The review of detailed 1990 information indicated that respondents tended to provide their age as of the date of completion of the questionnaire, not their age as of April 1, 1990. In addition, there may have been a tendency for respondents to round-up their age if they were close to having a birthday. A detailed explanation of the age modification procedure appears in 1990 Census of Population and Housing Data Paper Listing (CPHL- 74).

Population estimates and projections are published in the P25 Series of CurrentPopulation Reports and on the Census Bureau Internet site http://www.census.gov/. These estimates and projections are generally consistent with official decennial census figures and do not reflect the amount of estimated census underenumeration. However, these estimates and projections by race have been modified and are not comparable to the census race categories (see section below under ‘‘Race’’). For details on methodology, see the sources cited below the individual tables.

Immigration-The principal source of immigration data is the Statistical Yearbookof the Immigration and NaturalizationService, published annually by the Immigration and Naturalization Service (INS), a unit of the Department of Justice. Immigration statistics are prepared from entry visas and change of immigration status forms. Immigrants are aliens admitted for legal permanent residence in the United States. The procedures for admission depend on whether the alien is residing inside or outside the United States at the time of application for permanent residence. Eligible aliens residing outside the United States are issued immigrant visas by the U.S. Department of State. Eligible aliens residing in the United States are allowed to change their status from temporary to permanent residence at INS district offices. The category, immigrant, includes persons who may have entered the United States as nonimmigrants or refugees, but who subsequently changed their status to that of a permanent resident. Nonresident aliens admitted to the United States for a temporary period are nonimmigrants (Table 1243). Refugees are considered nonimmigrants when initially admitted into the United States but are not included in nonimmigrant admission data. A refugee is an alien outside the United States who is unable or unwilling to return to his or her county of nationality because of persecution or a wellfounded fear of persecution.

U.S. immigration law gives preferential immigration status to persons with a close family relationship with a U.S. citizen or legal permanent resident, persons with needed job skills, or persons who qualify as refugees. Immigration to the United States can be divided into two general categories: (1) those subject to the annual worldwide limitation and (2) those exempt from it. The Immigration Act of 1990 established major revisions in the numerical limits and preference system regulating legal immigration. The numerical limits are imposed on visas issued and not on admissions. The maximum number of visas allowed to be issued under the preference categories in 2000 was 436,900 - 294,601 for family-sponsored immigrants and 142,299 for employment based immigrants. There are nine categories among which the family-sponsored and employment-based immigrant visas are distributed, beginning in fiscal year 1992. The family-sponsored preferences are based on the alien’s relationship with a U.S. citizen or legal permanent resident (see Table 6). The employment-based preferences are (1) priority workers (persons of extraordinary ability, outstanding professors and researchers, and certain multinational executives and managers); (2) professionals with advanced degrees or aliens with exceptional ability; (3) skilled workers, professionals without advanced degrees, and needed unskilled workers; (4) special immigrants; and (5) employment creation immigrants (investors). Within the overall limitations the per-country limit for independent countries is set to 7 percent of the total family sponsored and employment-based limits, while dependent areas are limited to 2 percent of the total. The 2000 limit allowed no more than 30,583 preference visas for any independent country and 8,738 for any dependency. Those exempt from the worldwide limitation include immediate relatives of U.S. citizens, refugees and asylees adjusting to permanent residence, and other various classes of special immigrants (see Table 6).

The Refugee Act of 1980, effective April 1, 1980, provides for a uniform admission procedure for refugees of all countries, based on the United Nations’ definition of refugees. Authorized admission ceilings are set annually by the President in consultation with Congress. After 1 year of residence in the United States, refugees are eligible for immigrant status. The Immigration Reform and Control Act of 1986 (IRCA) allows two groups of illegal aliens to become temporary and then permanent residents of the United States: aliens who have been in the United States unlawfully since January 1, 1982 (legalization applicants), and aliens who were employed in seasonal agricultural work for a minimum period of time (Special Agricultural Worker (SAW) applicants). The application period for temporary residency for legalization applicants began on May 5, 1987, and ended on May 4, 1988, while the application period for SAW applicants began on June 1, 1987, and ended on November 30, 1988. Legalization applicants became eligible for permanent residence beginning in fiscal year 1989. Beginning 1989 immigrant data include temporary residents who were granted permanent residence under the legalization program of IRCA.

Metropolitan Areas (MAs)-The general concept of a metropolitan area is one of a core area containing a large population nucleus, together with adjacent communities that have a high degree of social and economic integration with that core. Metropolitan statistical areas (MSAs), consolidated metropolitan statistical areas (CMSAs), and primary metropolitan statistical areas (PMSAs) are defined by the Office of Management and Budget (OMB) as a standard for federal agencies in the preparation and publication of statistics relating to metropolitan areas. The entire territory of the United States is classified as metropolitan (inside MSAs or CMSAs- PMSAs are components of CMSAs) or nonmetropolitan (outside MSAs or CMSAs). MSAs, CMSAs, and PMSAs are defined in terms of entire counties except in New England, where the definitions are in terms of county subdivisions (primarily cities and towns). The OMB also defines New England County Metropolitan Areas (NECMAs), which are county-based alternatives to the MSAs and CMSAs in the six New England states. Over time, new MAs are created and the components of others change. The analysis of historical trends, therefore, must be made cautiously. For descriptive details and a listing of titles and components of MAs, see Appendix II.

Urban and rural-For Census 2000, the Census Bureau classified as urban all territory, population, and housing units located within urbanized areas (UAs) and urban clusters (UCs). A UA consists of densely settled territory that contains 50,000 or more people, while a UC consists of densely settled territory with at least 2,500 people but fewer than 50,000 people. (UCs are a new type of geographic entity for Census 2000.) Prior to Census 2000-from the 1950 census through the 1990 census-the urban population consisted of all people living in UAs and most places outside of UAs with a census population of 2,500 or more.

UAs and UCs encompass territory thatgenerally consists of:

• A cluster of one or more block goups or census blocks each of which has a population density of at least 1,000 people per square mile at the time,

• Surrounding block groups and census blocks each of which has a population density of at least 500 people per square mile at the time, and

• Less densely settled blocks that form enclaves or indentations, or are used to connect discontiguous areas with qualifying densities.

They also may include an airport located adjacent to qualifying densely settled area if it has an annual enplanement (aircraft boarding) of at least 10,000 people.

‘‘Rural’’ for Census 2000 consists of all territory, population, and housing units located outside of UAs and UCs. Prior to Census 2000, rural consisted of all territory, population, and housing outside of UAs and outside of other places designated as ‘‘urban.’’ For Census 2000, many more geographic entities, including metropolitan areas, counties, county subdivisions, and places, contain both urban and rural territory, population, and housing units.

Residence-In determining residence, the Census Bureau counts each person as an inhabitant of a usual place of residence (i.e., the place where one usually lives and sleeps). While this place is not necessarily a person’s legal residence or voting residence, the use of these different bases of classification would produce the same results in the vast majority of cases.

Race-For the 1990 census, the Census Bureau collected and published racial statistics as outlined in Statistical Policy Directive No. 15 issued by the U.S. Office of Management and Budget. This directive provided standards on ethnic and racial categories for statistical reporting to be used by all federal agencies. According to the directive, the basic racial categories were American Indian or Alaska Native, Asian or Pacific Islander, Black, and White. (The directive identified Hispanic origin as an ethnicity.) The question on race for Census 2000 was different from the one for the 1990 census in several ways. Most significantly, respondents were given the option of selecting one or more race categories to indicate their racial identities. Because of these changes, the Census 2000 data on race are not directly comparable with data from the 1990 census or earlier censuses. Caution must be used when interpreting changes in the racial composition of the U.S. population over time. Census 2000 adheres to the federal standards for collecting and presenting data on race and Hispanic origin as established by the Office of Management and Budget (OMB) in October 1997. Starting with Census 2000, the OMB requires federal agencies to use a minimum of five race categories: White, Black or African American, American Indian or Alaska Native, Asian, and Native Hawaiian or Other Pacific Islander. For respondents unable to identify with any of these five race categories, OMB approved and included a sixth category-‘‘Some other race’’-on the Census 2000 questionnaire. The Census 2000 question on race included 15 separate response categories and three areas where respondents could write in a more specific race group. The response categories and write-in answers can be combined to create the five minimum OMB race categories plus ‘‘Some other race.’’ People who responded to the question on race by indicating only one race are referred to as the race alonepopulation, or the group that reported only one race category. Six categories make up this population: White alone;Black or African American alone; American Indian and Alaska Native alone; Asian alone; Native Hawaiian and Other Pacific Island alone; and Some other race alone.Individuals who chose more than one of the six race categories are referred to as the Two or more races population, or as the group that reported more than one race.

The concept of race the Census Bureau uses reflects self-identification by respondents; that is the individual’s perception of his/her racial identity. The concept is not intended to reflect any biological or anthropological definition. Furthermore, the Census Bureau recognizes that the categories of the race item include both racial and national origin or sociocultural groups.

Data for the population by race for April 1, 1990 (shown in Table 10) are modified counts and are not comparable to the 1990 census race categories. These numbers were computed using 1990 census data by race which had been modified to be consistent with the guidelines in Federal Statistical Policy Directive No. 15 issued by the Office of Management and Budget. A detailed explanation of the race modification procedure appears in 1990Census of Population and Housing Data Paper Listing (CPH-L-74).

In the CPS and other household sample surveys in which data are obtained through personal interview, respondents are asked to classify their race as: (1) White; (2) Black; (3) American Indian, Aleut, or Eskimo; or (4) Asian or Pacific Islander. The procedures for classifying persons of mixed races who could not provide a single response to the race question are generally similar to those used in the census.

Hispanic population-The question on Hispanic origin for Census 2000 was similar to the 1990 census question, except for its placement on the questionnaire. For Census 2000, the question on Hispanic origin was asked directly before the question on race. For the 1990 census, the order was reversed-the question on race preceded questions on age and marital status, which were followed by the question on Hispanic origin. In the 1990 census, the Census Bureau collected data on the Hispanic origin population in the United States by using a self-identification question. Persons of Spanish/Hispanic origin are those who classified themselves in one of the specific Hispanic origin categories listed on the questionnaire -Mexican, Puerto Rican, Cuban, as well as those who indicated that they were of Other Spanish/Hispanic origin. Persons of Other Spanish/Hispanic origin are those whose origins are from Spain, the Spanish-speaking countries of Central or South America, or the Dominican Republic.In 1980, 1990, and 2000, the Hispanic-origin question contained prelisted categories for the largest Hispanic-origin groups-Mexican, Puerto Rican, Cuban, and Other Spanish/Hispanic. The 1990 Hispanic-origin questiondiffered from the 1980 question in that it contained a write-in line for the Other Spanish/Hispanic category. This was coded only for sample data. Another difference between the 1980 and 1990 Hispanic-origin question is that in 1980 the wording of the Hispanic-origin question read: ‘‘Is this person of Spanish/ Hispanic origin or descent?’’ while in 1990 the word ‘‘descent’’ was dropped from the question. Persons of Hispanic origin may be of any race.

In the CPS information on Hispanic persons is gathered by using a selfidentification question. Persons classify themselves in one of the Hispanic categories in response to the question: ’’What is the origin or descent of each person in this household?’’ Hispanic persons in the CPS are persons who report themselves as Mexican-American, Chicano, Mexican, Puerto Rican, Cuban, Central or South American (Spanish countries), or other Hispanic origin.

Nativity-The native population consists of all persons born in the United States, Puerto Rico, or an outlying area of the United States. It also includes persons born in a foreign country who had at least one parent who was a U.S. citizen. All other persons are classified as ‘‘foreign born.’’

Mobility status-The U.S. population is classified according to mobility status on the basis of a comparison between the place of residence of each individual at the time of the survey or census and the place of residence at a specified earlier date. Nonmovers are all persons who were living in the same house or apartment at the end of the period as at the beginning of the period. Movers are all persons who were living in a different house or apartment at the end of the period than at the beginning of the period. Movers are further classified as to whether they were living in the same or different county, state, or region or were movers from abroad. Movers from abroad include all persons, either U.S. citizens or non-citizens, whose place of residence was outside the United States at the beginning of the period; that is, in Puerto Rico, an outlying area under the jurisdiction of the United States, or a foreign country.

Living arrangements-Living arrangements refer to residency in households or in group quarters. A ’’household’’ comprises all persons who occupy a ’’housing unit,’’ that is, a house, an apartment or other group of rooms, or a single room that constitutes ’’separate living quarters.’’ A household includes the related family members and all the unrelated persons, if any, such as lodgers, foster children, wards, or employees who share the housing unit. A person living alone or a group of unrelated persons sharing the same housing unit is also counted as a household. See text, Section 20, Construction and Housing, for definition of housing unit.

All persons not living in housing units are classified as living in group quarters. These individuals may be institutionalized, e.g., under care or custody in juvenile facilities, jails, correctional centers, hospitals, or nursing homes; or they may be residents in noninstitutional group quarters such as college dormitories, group homes, or military barracks.

Householder-The householder is the first adult household member listed on the questionnaire. The instructions call for listing first the person (or one of the persons) in whose name the home is owned or rented. If a home is owned or rented jointly by a married couple, either the husband or the wife may be listed first. Prior to 1980, the husband was always considered the household head (householder) in married couple households.

Family-The term family refers to a group of two or more persons related by birth, marriage, or adoption and residing together in a household. A family includes among its members the householder.

Subfamily-A subfamily consists of a married couple and their children, if any, or one parent with one or more nevermarriedchildren under 18 years old living in a household. Subfamilies are divided into ’’related’’ and ’’unrelated’’ subfamilies. A related subfamily is related to, but does not include, the householder. Members of a related subfamily are also members of the family with whom they live. The number of related subfamilies, therefore, is not included in the count of families. An unrelated subfamily may include persons such as guests, lodgers, or resident employees and their spouses and/or children; none of whom is related to the householder.

Married couple-A married couple is defined as a husband and wife living together in the same household, with or without children and other relatives.

Statistical reliability-For a discussion of statistical collection and estimation, sampling procedures, and measures of statistical reliability applicable to Census Bureau data, see Appendix III.