Documentation: Census 2000
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Publisher: U.S. Census Bureau
Survey: Census 2000
Document: Summary File 1 Technical Documentation
citation:
Social Explorer, U.S. Census Bureau; 2000 Census of Population and Housing, Summary File 1: Technical Documentation, 2001.
Chapter Contents
Population Characteristics
Group Quarters
Summary File 1 Technical Documentation
Appendix B. Definitons of Subject Characteristics
Population Characteristics
The data on age were derived from answers to a question that was asked of all people. The age classification is based on the age of the person in complete years as of April 1, 2000. The age of the person was usually derived from their date of birth information. Their reported age was used only when date of birth information was unavailable.

Data on age are used to determine the applicability of some of the sample questions for a person and to classify other characteristics in census tabulations. Age data are needed to interpret most social and economic characteristics used to plan and examine many programs and policies.

Median age
This measure divides the age distribution into two equal parts: one-half of the cases falling below the median value and one-half above the value. Median age is computed on the basis of a single year of age distribution.

Limitation of the data
The most general limitation for many decades has been the tendency of people to overreport ages or years of birth that end in zero or five. This phenomenon is called "age heaping." In addition, the counts in the 1970 and 1980 censuses for people 100 years old and over were substantially overstated. So also were the counts of people aged 69 in 1970 and aged 79 in 1980. Improvements have been made since then in the questionnaire design, and in the allocation procedures which have further minimized these problems. The count of people aged 89 in the 1990 census was not overstated.

Review of detailed 1990 census information indicated that respondents tended to provide their age as of the date they completed the questionnaire, not their age as of April 1, 1990. One reason this happened was that respondents were not specifically instructed to provide their age as of April 1, 1990. Another reason was that data collection efforts continued well past the census date. In addition, there may have been a tendency for respondents to round their age up if they were close to having a birthday. It is likely that approximately 10 percent of people in most age groups were actually one year younger. For most single years of age, the misstatements were largely offsetting. The problem is most pronounced at age zero because people lost to age one probably were not fully offset by the inclusion of babies born after April 1, 1990. Also, there may have been more rounding up to age one to avoid reporting age as zero years. (Age in complete months was not collected for infants under age one.)

The reporting of age one year older than true age on April 1, 1990, is likely to have been greater in areas where the census data were collected later in calendar year 1990. The magnitude of this problem was much less in the 1960, 1970, and 1980 censuses where age was typically derived from respondent data on year of birth and quarter of birth.

These shortcomings were minimized in Census 2000 because age was usually calculated from exact date of birth and because respondents were specifically asked to provide their age as of April 1, 2000. (For more information on the design of the age question, see the section below that discusses "Comparability.")

Comparability
Age data have been collected in every census. For the first time since 1950, the 1990 data were not available by quarter year of age. This change was made so that coded information could be obtained for both age and year of birth. In 2000, each individual has both an age and an exact date of birth. In each census since 1940, the age of a person was assigned when it was not reported. In censuses before 1940, with the exception of 1880, people of unknown age were shown as a separate category. Since 1960, assignment of unknown age has been performed by a general procedure described as "imputation." The specific procedures for imputing age have been different in each census. (For more information on imputation, see "Accuracy of the Data.")
For more information on age, please telephone 301-457-2428.

Group Quarters
All people not living in housing units are classified by the Census Bureau as living in group quarters. We recognize two general categories of people in group quarters: (1) institutionalized population and (2) noninstitutionalized population.

Institutionalized population
Includes people under formally authorized, supervised care or custody in institutions at the time of enumeration. Such people are classified as "patients or inmates" of an institution regardless of the availability of nursing or medical care, the length of stay, or the number of people in the institution. Generally, the institutionalized population is restricted to the institutional buildings and grounds (or must have passes or escorts to leave) and thus have limited interaction with the surrounding community. Also, they are generally under the care of trained staff who have responsibility for their safekeeping and supervision.

Type of institution
The type of institution was determined as part of census enumeration activities. For institutions that specialize in only one specific type of service, all patients or inmates were given the same classification. For institutions that had multiple types of major services (usually general hospitals and Veterans Administration hospitals), patients were classified according to selected types of wards. For example, in psychiatric wards of hospitals, patients were classified in "mental (psychiatric) hospitals"; in general hospital wards for people with chronic diseases, patients were classified in "other hospitals for the chronically ill." Each patient or inmate was classified in only one type of institution. Institutions include the following types:

Correctional institutions
Includes prisons, federal detention centers, military disciplinary barracks and jails, police lockups, halfway houses used for correctional purposes, local jails, and other confinement facilities, including work farms.

Prisons
Where people convicted of crimes serve their sentences. In some census products, the prisons are classified by two types of control: (1) "federal" (operated by the Bureau of Prisons of the Department of Justice) and (2) "state." In census products this category includes federal detention centers. Residents who are criminally insane were classified on the basis of where they resided at the time of enumeration: (1) in institutions (or hospital wards) operated by departments of correction or similar agencies, or (2) in institutions operated by departments of mental health or similar agencies.

Federal detention centers
Operated by the Immigration and Naturalization Service (INS) and the Bureau of Prisons. These facilities include: detention centers used by the Park Police; Bureau of Indian Affairs Detention Centers; INS Centers, such as the INS Federal Alien Detention Facility; INS Processing Centers; INS Contract Detention Centers used to detain aliens under exclusion or deportation proceedings, as well as those aliens who have not been placed into proceedings, such as custodial required departures; and INS Detention Centers operated within local jails, and state and federal prisons.

Military disciplinary barracks and jails
Operated by military police and used to hold people awaiting trial or convicted of violating military laws.

Local jails and other confinement facilities
Includes facilities operated by counties and cities that primarily hold people beyond arraignment, usually for more than 48 hours and police lockups operated by county and city police that hold people for 48 hours or less only if they have not been formally charged in court. Also, includes work farms used to hold people awaiting trial or serving time on relatively short sentences and jails run by private businesses under contract for local governments (but not by state governments).

Halfway houses
Operated for correctional purposes and include probation and restitution centers, prerelease centers, and community-residential centers.

Other types of correctional institutions
Privately operated correctional facilities and correctional facilities specifically for alcohol or drug abuse.

Nursing homes
Comprises a heterogeneous group of places providing continuous nursing and other services to patients. The majority of patients are elderly, although people who require nursing care because of chronic physical conditions may be found in these homes regardless of their age. Included in this category are skilled-nursing facilities, intermediate-care facilities, long-term care rooms in wards or buildings on the grounds of hospitals, or long-term care rooms/nursing wings in congregate housing facilities. Also included are nursing, convalescent, and rest homes, such as soldiers, sailors, veterans, and fraternal or religious homes for the aged, with nursing care.

Mental (psychiatric) hospitals
Includes hospitals or wards for the criminally insane not operated by a prison and psychiatric wards of general hospitals and veterans hospitals. Patients receive supervised medical/nursing care from formally trained staff.

Hospitals or wards for chronically ill
Includes hospitals for patients who require long-term care, including those in military hospitals and wards for the chronically ill located on military bases; or other hospitals or wards for the chronically ill, which include tuberculosis hospitals or wards; wards in general and Veterans Administration hospitals for the chronically ill; neurological wards; hospices and homes for chronically ill patients; wards for patients with Hansens Disease (leprosy) and other incurable diseases; and other unspecified wards for the chronically ill. Patients who had no usual home elsewhere were enumerated as part of the institutional population in the wards of general and military hospitals. Most hospital patients are at the hospital temporarily and were enumerated at their usual place of residence. In some census products, patients in hospitals or wards for the chronically ill are classified in three categories: (1) military hospitals or wards for chronically ill, (2) other hospitals or wards for chronically ill, and (3) hospices or homes for chronically ill.

Schools, hospitals, or wards for the mentally retarded
Includes those institutions such as wards in hospitals for the mentally retarded and intermediate-care facilities for the mentally retarded that provide supervised medical/nursing care from formally trained staff.

Schools, hospitals, orwar ds forthe physically handicapped
Includes three types of institutions: institutions for the blind, those for the deaf, and orthopedic wards and institutions for the physically handicapped. Institutions for people with speech problems are classified with "institutions for the deaf." The category "orthopedic wards and institutions for the physically handicapped" includes those institutions providing relatively long-term care to accident victims and to people with polio, cerebral palsy, and muscular dystrophy.

Hospitals and wards for drug/alcohol abuse
Includes hospitals and wards for drug/alcohol abuse. These facilities are equipped medically and designed for the diagnosis and treatment of medical or psychiatric illnesses associated with alcohol or drug abuse. Patients receive supervised medical care from formally trained staff.

Wards in general hospitals for patients who have no usual home elsewhere
Includes maternity, neonatal, pediatric (including wards for boarder babies), and surgical wards of hospitals and wards for people with infectious diseases. If not shown separately, this category includes wards in military hospitals for patients who have no usual home elsewhere.

Wards in military hospitals for patients who have no usual home elsewhere
(See above definition for "Wards in general hospitals for patients who have no usual home elsewhere.")

Juvenile institutions
Includes homes, schools, and other institutions providing care for children (short- or long-term care). Juvenile institutions include the following types:

Homes for abused, dependent, and neglected children
Includes orphanages and other institutions that provide long-term care (usually more than 30 days) for children.

Residential treatment centers
Includes those institutions that primarily serve children who, by clinical diagnosis, are moderately or seriously disturbed emotionally. Also, these institutions provide long-term treatment services, usually supervised or directed by a psychiatrist. Training schools for juvenile delinquents. Includes residential training schools or homes, and industrial schools, camps, or farms for juvenile delinquents.

Public training schools for juvenile delinquents
Usually operated by a state agency (for example, department of welfare, corrections, or a youth authority). Some are operated by county and city governments. These public training schools are specialized institutions serving delinquent children, generally between the ages of 10 and 17 years old, all of whom are committed by the courts.

Private training schools
Operated under private auspices. Some of the children they serve are committed by the courts as delinquents. Others are referred by parents or social agencies because of delinquent behavior. One difference between private and public training schools is that, by their administrative policy, private schools have control over their selection and intake.

Detention centers
Includes institutions providing short-term care (usually 30 days or less) primarily for delinquent children pending disposition of their cases by a court. This category also covers diagnostic centers. In practice, such institutions may be caring for both delinquent and neglected children pending court disposition.

Noninstitutionalized population
Includes people who live in group quarters other than institutions. Includes staff residing in military and nonmilitary group quarters on institutional grounds who provide formally authorized, supervised care or custody for the institutionalized population.

Group Homes
Includes "community-based homes" that provide care and supportive services. Such places include homes for the mentally ill, mentally retarded, and physically handicapped; drug/alcohol halfway houses not operated for correctional purposes; communes; and maternity homes for unwed mothers.

Homes for the mentally ill
Includes community-based homes that provide care primarily for the mentally ill. Homes that combine treatment of the physically handicapped with treatment of the mentally ill are counted as homes for the mentally ill.

Homes for the mentally retarded
Includes community-based homes that provide care primarily for the mentally retarded. Homes that combine treatment of the physically handicapped with treatment of the mentally retarded are counted as homes for the mentally retarded.

Homes for the physically handicapped
Includes community-based homes for the blind, for the deaf, and other community-based homes for the physically handicapped. People with speech problems are classified with homes for the deaf. Homes that combine treatment of the physically handicapped with treatment of the mentally ill are counted as homes for the mentally ill. Homes that combine treatment of the physically handicapped with treatment of the mentally retarded are counted as homes for the mentally retarded.

Homes or halfway houses for drug/alcohol abuse
Includes people with no usual home elsewhere in places that provide community-based care and supportive services to people suffering from a drug/alcohol addiction and to recovering alcoholics and drug abusers. Places providing community-based care for drug and alcohol abusers include group homes, detoxification centers, quarterway houses (residential treatment facilities that work closely with accredited hospitals), halfway houses, and recovery homes for ambulatory, mentally competent recovering alcoholics and drug abusers who may be reentering the work force.

Other group homes
Includes people with no usual home elsewhere in communes, foster care homes, and maternity homes for unwed mothers. Most of these types of places provide communal living quarters, generally for people who have formed their own community in which they have common interests and often share or own property jointly. The maternity homes for unwed mothers provide domestic care for unwed mothers and their children. These homes may provide social services and postnatal care within the facility, or may make arrangements for women to receive such services in the community. Nursing services are usually available in the facility.

Religious group quarters
Includes, primarily, group quarters for nuns teaching in parochial schools and for priests living in rectories. It also includes other convents and monasteries, except those associated with a general hospital or an institution.

College quarters off campus
Includes university-owned off-campus housing, if the place is reserved exclusively for occupancy by college students who do not have their families living with them. In census products, people in this category are classified as living in a college dormitory.

College dormitories
Includes college students in dormitories (provided the dormitory is restricted to students who do not have their families living with them), fraternity and sorority houses, and on-campus residential quarters used exclusively for those in religious orders who are attending college. College dormitory housing includes university-owned, on-campus and off-campus housing for unmarried residents.

Military quarters
Includes military personnel living in barracks and dormitories on base, transient quarters on base for temporary residents (both civilian and military), and military ships. However, patients in military hospitals receiving treatment for chronic diseases or who had no usual home elsewhere, and people being held in military disciplinary barracks were included as part of the institutionalized population.

Agriculture workers' dormitories
Includes people in migratory farm workers camps on farms, bunkhouses for ranch hands, and other dormitories on farms, such as those on "tree farms." (A tree farm is an area of forest land managed to ensure continuous commercial production.)
Other workers' dormitories
Includes people in logging camps, construction workers camps, firehouse dormitories, job-training camps, energy enclaves (Alaska only), and nonfarm migratory workers camps (for example, workers in mineral and mining camps).

Dormitories for nurses and interns in general and military hospitals
Includes group quarters for nurses and other staff members, excluding patients. If not shown separately, dormitories for nurses and interns in general and military hospitals are included in the category "Staff Residents of Institutions."

Job corps and vocational training facilities
Includes facilities that provide a full-time, year-round residential program offering a comprehensive array of training, education, and supportive services, including supervised dormitory housing, meals, and counseling for at-risk youth ages 16 through 24.

Emergency and transitional shelters (with sleeping facilities)
Includes people without conventional housing who stayed overnight on March 27, 2000, in permanent and emergency housing, missions, Salvation Army shelters, transitional shelters, hotels and motels used to shelter people without conventional housing, and similar places known to have people without conventional housing staying overnight. Also included are shelters that operate on a first come, first-serve basis where people must leave in the morning and have no guaranteed bed for the next night OR where people know that they have a bed for a specified period of time (even if they leave the building every day). Shelters also include facilities that provide temporary shelter during extremely cold weather (such as churches). If shown, this category also includes shelters for children who are runaways, neglected, or without conventional housing.

Shelters for children who are runaways, neglected, or without conventional housing
Includes shelters/group homes that provide temporary sleeping facilities for juveniles. In census products, this category is included with emergency and transitional housing.

Shelters for abused women (shelters against domestic violence or family crisis centers)
Includes community-based homes or shelters that provide domiciliary care for women who have sought shelter from family violence and who may have been physically abused. Most shelters also provide care for children of abused women. These shelters may provide social services, meals, psychiatric treatment, and counseling. In census products, this category is included with "other noninstitutional group quarters."

Soup kitchens
Includes soup kitchens, food lines, and programs distributing prepared breakfasts, lunches, or dinners on March 28, 2000. These programs may be organized as food service lines, bag or box lunches, or tables where people are seated, then served by program personnel. These programs may or may not have a place for clients to sit and eat the meal. In census products, this category is included with "other noninstitutional group quarters." This category excludes regularly scheduled mobile food vans.

Regularly scheduled mobile food vans
Includes mobile food vans that are regularly scheduled to visit designated street locations for the primary purpose of providing food to people without conventional housing. In census products, this category is included with "other noninstitutional group quarters."

Targeted nonsheltered outdoor locations
Includes geographically identifiable outdoor locations open to the elements where there is evidence that people who do not usually receive services at soup kitchens, shelters, and mobile food vans lived on March 29, 2000, without paying to stay there. Sites must have a specific location description that allowed a census enumeration team to physically locate the site; for example, "the Brooklyn Bridge at the corner of Bristol Drive" or "the 700 block of Taylor Street behind the old warehouse." Excludes pay-for-use campgrounds; drop-in centers; post offices; hospital emergency rooms; and commercial sites, including all-night theaters and all-night diners. In census products, this category is included with "other noninstitutional group quarters."

Crews of maritime vessels
Includes officers, crew members, and passengers of maritime U.S. flag vessels. All ocean-going and Great Lakes ships are included.

Residential facilities providing "protective oversight"
Includes facilities providing assistance to people with disabilities.

Staff residents of institutions
Includes staff residing in military and nonmilitary group quarters on institutional grounds who provide formally authorized, supervised care or custody for the institutionalized population.

Other nonhousehold living situations
Includes people with no usual home elsewhere enumerated at locations such as YMCAs, YWCAs, and hostels. People enumerated at those places that did not have a usual home elsewhere are included in this category.

Living quarters for victims of natural disasters
Includes living quarters for people temporarily displaced by natural disasters.

Comparability
For Census 2000, the definition of the institutionalized population was consistent with the definition used in the 1990 census. As in 1990, the definition of "care" only includes people under organized medical or formally authorized, supervised care or custody.

In Census 2000, the 1990 and 1980 rule of classifying ten or more unrelated people living together as living in noninstitutional group quarters was dropped. In 1970, the criteria was six or more unrelated people.

Several changes have occurred in the tabulation of specific types of group quarters. In Census 2000, police lockups were included with local jails and other confinement facilities, and homes for unwed mothers were included in "Other group homes;" in 1990, these categories were shown separately. For the first time, Census 2000 tabulates separately the following types of group quarters: military hospitals or wards for the chronically ill, other hospitals or wards for the chronically ill, hospices or homes for the chronically ill, wards in military hospitals with patients who have no usual home elsewhere, wards in general hospitals with patients who have no usual home elsewhere, and job corps and vocational training facilities. For Census 2000, rooming and boarding houses were classified as housing units rather than group quarters as in 1990.

As in 1990, workers dormitories were classified as group quarters regardless of the number of people sharing the dormitory. In 1980, ten or more unrelated people had to share the dorm for it to be classified as a group quarters. In 1960, data on people in military barracks were shown only for men. In subsequent censuses, they include both men and women.

The phrase "institutionalized persons" in 1990 data products was changed to "institutionalized population" for Census 2000. In 1990, the Census Bureau used the phrase "other persons in group quarters" for people living in noninstitutional group quarters. In 2000, this group is referred to as the "noninstitutionalized population." The phrase "staff residents" was used for staff living in institutions in both 1990 and 2000.

In Census 2000, the category "emergency and transitional shelters" includes emergency shelters, transitional shelters, and shelters for children who are runaways, neglected, or without conventional housing. Those people tabulated at shelters for abused women, soup kitchens, regularly scheduled mobile food vans, and targeted nonsheltered outdoor locations were included in the category "other noninstitutional group quarters." Each of these categories were enumerated from March 27-29, 2000, during Service-Based enumeration. (For more information on the "Service- Based Enumeration" operation, see "Collection and Processing Procedures.")
For more information on group quarters, please telephone 301-457-2378.

Hispanic or Latino
The data on the Hispanic or Latino population were derived from answers to a question that was asked of all people. The terms "Spanish,""Hispanic origin," and "Latino" are used interchangeably. Some respondents identify with all three terms while others may identify with only one of these three specific terms. Hispanics or Latinos who identify with the terms "Spanish,"" Hispanic," or "Latino" are those who classify themselves in one of the specific Spanish, Hispanic, or Latino categories listed on the questionnaire ("Mexican,""Puerto Rican," or "Cuban") as well as those who indicate that they are "other Spanish/Hispanic/Latino." People who do not identify with one of the specific origins listed on the questionnaire but indicate that they are "other Spanish, Hispanic, or Latino" are those whose origins are from Spain, the Spanish-speaking countries of Central or South America, the Dominican Republic, or people identifying themselves generally as Spanish, Spanish-American, Hispanic, Hispano, Latino, and so on. All write-in responses to the "other Spanish/Hispanic/Latino" category were coded.

Origin can be viewed as the heritage, nationality group, lineage, or country of birth of the person or the persons parents or ancestors before their arrival in the United States. People who identify their origin as Spanish, Hispanic, or Latino may be of any race. Some tabulations are shown by the origin of the householder. In all cases where the origin of households, families, or occupied housing units is classified as Spanish, Hispanic, or Latino, the origin of the householder is used. (See the discussion of householder under "Household Type and Relationship.")

If an individual could not provide a Hispanic origin response, their origin was assigned using specific rules of precedence of household relationship. For example, if origin was missing for a natural-born daughter in the household, then either the origin of the householder, another naturalborn child, or spouse of the householder was assigned. If Hispanic origin was not reported for anyone in the household, the Hispanic origin of a householder in a previously processed household with the same race was assigned. This procedure is a variation of the general imputation procedures described in "Accuracy of the Data" and is similar to those used in 1990, except for Census 2000 race and Spanish surnames were used to assist in assigning an origin (see the "Comparability" section below also).

Comparability
There are two important changes to the Hispanic origin question for Census 2000. First, the sequence of the race and Hispanic origin questions for Census 2000 differs from that in 1990; in 1990, the race question preceded the Hispanic origin question. Testing prior to Census 2000 indicated that response to the Hispanic origin question could be improved by placing it before the race question without affecting the response to the race question. Second, there is an instruction preceding the Hispanic origin question indicating that respondents should answer both the Hispanic origin and the race questions. This instruction was added to give emphasis to the distinct concepts of the Hispanic origin and race questions, and to emphasize the need for both pieces of information.

Furthermore, there has been a change in the processing of the Hispanic origin and race responses. In the 1990 census, respondents provided Hispanic origin responses in the race question and race responses in the Hispanic origin question. In 1990, the Hispanic origin question and the race question had separate edits; therefore, although information may have been present on the questionnaire, it was not fully utilized due to the discrete nature of the edits. However, for Census 2000 there is a joint race and Hispanic origin edit, which can utilize Hispanic origin and race information that was reported in the inappropriate question.
For more information on Hispanic or Latino, please telephone 301-457-2403.

Household Type and Relationship
Household
A household includes all of the people who occupy a housing unit. A housing unit is a house, an apartment, a mobile home, a group of rooms, or a single room occupied (or if vacant, intended for occupancy) as separate living quarters. Separate living quarters are those in which the occupants live separately from any other people in the building and that have direct access from the outside of the building or through a common hall. The occupants may be a single family, one person living alone, two or more families living together, or any other group of related or unrelated people who share living quarters.

In 100-percent tabulations, the count of households or householders always equals the count of occupied housing units. In sample tabulations, the numbers may differ as a result of the weighting process.

Average household size
A measure obtained by dividing the number of people in households by the number of households (or householders). In cases where household members are tabulated by race or Hispanic origin, household members are classified by the race or Hispanic origin of the householder rather than the race or Hispanic origin of each individual.

Relationship to Householder
The phrase "Coverage Improvement Adjustment" was included in the table outlines and the technical documentation before the review, analysis, and recommendation on whether to adjust Census 2000 data for coverage improvement was completed. As the data are not adjusted, a zero (0) will appear. This phrase does not refer to any other outreach or collection opertions that were introduced to improve coverage in Census 2000.

Householder
The data on relationship to householder were derived from the question "How is this person related to Person 1," which was asked of Persons 2 and higher in housing units. One person in each household is designated as the householder (Person 1). In most cases, this is the person, or one of the people, in whose name the home is owned, being bought, or rented. If there is no such person in the household, any household member 15 years old or over could be designated as the householder (that is, Person 1).

Households are classified by type according to the sex of the householder and the presence of relatives. Two types of householders are distinguished: family householders and nonfamily householders. A family householder is a householder living with one or more people related to him or her by birth, marriage, or adoption. The householder and all of the people in the household related to him or her are family members. A nonfamily householder is a householder living alone or with nonrelatives only.

Spouse (husband/wife)
Includes a person married to and living with a householder. This category includes people in formal marriages, as well as people in common-law marriages. The number of spouses is equal to the number of "married-couple families" or "married-couple households" in 100-percent tabulations. Marital status categories cannot be inferred from the 100- percent tabulations since the marital status item was not included on the 100-percent form.

Child
Includes a son or daughter by birth, a stepchild, or an adopted child of the householder, regardless of the childs age or marital status. The category excludes sons-in-law, daughters-inlaw, and foster children.

Natural-born son/daughter
A son or daughter of the householder by birth, regardless of the age of the child.

Adopted son/daughter
A son or daughter of the householder by legal adoption, regardless of the age of the child. If the stepson/stepdaughter of the householder has been legally adopted by the householder, the child is then classified as an adopted child.

Stepson/stepdaughter
A son or daughter of the householder through marriage but not by birth, regardless of the age of the child. If the stepson/stepdaughter of the householder has been legally adopted by the householder, the child is then classified as an adopted child.

Own child
A child under 18 years old who is a son or daughter by birth, marriage (a stepchild), or adoption. In certain tabulations, own children are further classified as living with two parents or with one parent only. For 100-percent tabulations, own children consist of all sons/daughters of householders who are under 18 years of age. For sample data, own children consist of sons/daughters of householders who are under 18 years of age and who have never been married, therefore, numbers of own children of householders may be different in these two tabulations.

"Related children" in a family include own children and all other people under 18 years of age in the household, who are related to the householder, except the spouse of the householder. Foster children are not included since they are not related to the householder.

Other relatives
Includes any household member related to the householder by birth, marriage, or adoption, but not included specifically in another relationship category. In certain detailed tabulations, the following categories may be shown:

Grandchild
The grandson or granddaughter of the householder.

Brother/sister
The brother or sister of the householder, including stepbrothers, stepsisters, and brothers and sisters by adoption. Brothers-in-law and sisters-in-law are included in the "Other relative" category on the questionnaire.

Parent
The father or mother of the householder, including a stepparent or adoptive parent. Fathers-in-law and mothers-in-law are included in the "Parent-in-law" category on the questionnaire.

Parent-in-law
Includes the mother-in-law or father-in-law of the householder.

Son-in-law/daughter-in-law
By definition, these are spouses of the children of the householder.

Other relatives
Anyone not listed in a reported category above who is related to the householder by birth, marriage, or adoption (brother-in-law, grandparent, nephew, aunt, cousin, and so forth).

Nonrelatives
Includes any household member who is not related to the householder by birth, marriage, or adoption, including foster children. The following categories may be presented in more detailed tabulations:

Roomer, boarder
Includes roomers or boarders, who live in a room in the household of Person 1 (householder). Some sort of cash or noncash payment (e.g., chores) is usually made for their living accommodations.

Housemate or roommate
A person who is not related to the householder and who shares living quarters primarily to share expenses.

Unmarried partner
A person who is not related to the householder, who shares living quarters, and who has a close personal relationship with the householder.

Foster child
Foster children are people under 18 placed by the local government in a household to receive parental care. They may be living in the household for just a brief period or for several years. Foster children are nonrelatives of the householder. If the foster child is also related to the householder, the child should be classified as that specific relative.

Other nonrelatives
A person who is not related by birth, marriage, or adoption to the householder and who is not described by the categories given above. When relationship is not reported for an individual, it is imputed according to the responses for the age and sex for that person while maintaining consistency with responses for other individuals in the household.

Unrelated Individual
An unrelated individual is: (1) a householder living alone or with nonrelatives only, (2) a household member who is not related to the householder, or (3) a person living in group quarters who is not an inmate of an institution.

Family Type
A family includes a householder and one or more other people living in the same household who are related to the householder by birth, marriage, or adoption. All people in a household who are related to the householder are regarded as members of his or her family. A household can contain only one family for purposes of census tabulations. Not all households contain families since a household may be a group of unrelated people or one person living alone.

Families are classified by type as either a "married-couple family" or an "other family" according to the presence of a spouse. "Other family" is further broken out according to the sex of the householder. The data on family type are based on answers to questions on sex and relationship that were asked on a 100-percent basis.

Married-couple family
A family in which the householder and his or her spouse are enumerated as members of the same household.

Other family
Male householder, no wife present
A family with a male householder and no spouse of the householder present.

Female householder, no husband present
A family with a female householder and no spouse of the householder present.

Nonfamily household
A householder living alone or with nonrelatives only.

Average family size
A measure obtained by dividing the number of people in families by the total number of families (or family householders). In cases where this measure is tabulated by race or Hispanic origin, the race or Hispanic origin refers to that of the householder rather than to the race or Hispanic origin of each individual.

Unmarried-Partner Household
An unmarried-partner household is a household other than a "married-couple household" that includes a householder and an "unmarried partner." An "unmarried partner" can be of the same sex or of the opposite sex of the householder. An "unmarried partner" in an "unmarried-partner household" is an adult who is unrelated to the householder, but shares living quarters and has a close personal relationship with the householder.

Comparability
The 1990 relationship category "Natural-born or adopted son/daughter" has been replaced by "Natural-born son/daughter" and "Adopted son/daughter." The following categories have been added: "Parent-in-law" and "Son-in-law/daughter-in-law." The 1990 nonrelative category, "Roomer, boarder, foster child" has been replaced by two categories, "Roomer, boarder" and "Foster child." In 2000, foster children had to be in the local governments' foster care system to be so classified. In 1990, foster children were estimated to be those children in households who were not related to the householder nor who had any people over 18 who may have been their parents. In 1990, stepchildren who were adopted by the householder were still classified as stepchildren. In 2000, stepchildren who were legally adopted by the householder were classified as adopted children.

For more information on household type or relationship to householder, please telephone 301-457-2416.

The data on race were derived from answers to the question on race that was asked of all people. The concept of race, as used by the Census Bureau, reflects self-identification by people according to the race or races with which they most closely identify. These categories are sociopolitical constructs and should not be interpreted as being scientific or anthropological in nature. Furthermore, the race categories include both racial and national-origin groups.

The racial classifications used by the Census Bureau adhere to the October 30, 1997, Federal Register Notice entitled, "Revisions to the Standards for the Classification of Federal Data on Race and Ethnicity" issued by the Office of Management and Budget (OMB). These standards govern the categories used to collect and present federal data on race and ethnicity. The OMB requires five minimum categories (White, Black or African American, American Indian or Alaska Native, Asian, and Native Hawaiian or Other Pacific Islander) for race. The race categories are described below with a sixth category, "Some other race," added with OMB approval. In addition to the five race groups, the OMB also states that respondents should be offered the option of selecting one or more races.

If an individual did not provide a race response, the race or races of the householder or other household members were assigned using specific rules of precedence of household relationship. For example, if race was missing for a natural-born child in the household, then either the race or races of the householder, another natural-born child, or the spouse of the householder were assigned. If race was not reported for anyone in the household, the race or races of a householder in a previously processed household were assigned. This procedure is a variation of the general imputation procedures described in "Accuracy of the Data."

White
A person having origins in any of the original peoples of Europe, the Middle East, or North Africa. It includes people who indicate their race as White or report entries such as Irish, German, Italian, Lebanese, Near Easterner, Arab, or Polish.

Black or African American
A person having origins in any of the Black racial groups of Africa. It includes people who indicate their race as Black, African Am., or Negro, or provide written entries such as African American, Afro American, Kenyan, Nigerian, or Haitian.

American Indian or Alaska Native
A person having origins in any of the original peoples of North and South America (including Central America) and who maintain tribal affiliation or community attachment. It includes people who classified themselves as described below.

American Indian
Includes people who indicated their race as "American Indian," entered the name of an Indian tribe, or reported such entries as Canadian Indian, French American Indian, or Spanish-American Indian.

American Indian tribe
Respondents who identified themselves as American Indian were asked to report their enrolled or principal tribe. Therefore, tribal data in tabulations reflect the written entries reported on the questionnaires. Some of the entries (for example, Iroquois, Sioux, Colorado River, and Flathead) represent nations or reservations. The information on tribe is based on self identification and therefore does not reflect any designation of federally or state-recognized tribe. Information on American Indian tribes is presented in summary files. The information for Census 2000 is derived from the American Indian Tribal Classification List for the 1990 census that was updated based on a December 1997 Federal Register Notice, entitled "Indian Entities Recognized and Eligible to Receive Service From the United States Bureau of Indian Affairs," Department of the Interior, Bureau of Indian Affairs, issued by the Office of Management and Budget.

Alaska Native
Includes written responses of Eskimos, Aleuts, and Alaska Indians as well as entries such as Arctic Slope, Inupiat, Yupik, Alutiiq, Egegik, and Pribilovian. The Alaska tribes are the Alaskan Athabascan, Tlingit, and Haida. The information for Census 2000 is based on the American Indian Tribal Classification List for the 1990 census, which was expanded to list the individual Alaska Native Villages when provided as a written response for race.

Asian
A person having origins in any of the original peoples of the Far East, Southeast Asia, or the Indian subcontinent including, for example, Cambodia, China, India, Japan, Korea, Malaysia, Pakistan, the Philippine Islands, Thailand, and Vietnam. It includes "Asian Indian," "Chinese," "Filipino," "Korean," "Japanese," "Vietnamese," and "Other Asian."

Asian Indian
Includes people who indicated their race as "Asian Indian" or identified themselves as Bengalese, Bharat, Dravidian, East Indian, or Goanese.

Chinese
Includes people who indicate their race as "Chinese" or who identify themselves as Cantonese, or Chinese American. In some census tabulations, written entries of Taiwanese are included with Chinese while in others they are shown separately.

Filipino
Includes people who indicate their race as "Filipino" or who report entries such as Philipino, Philipine, or Filipino American.

Japanese
Includes people who indicate their race as "Japanese" or who report entries such as Nipponese or Japanese American.

Korean
Includes people who indicate their race as "Korean" or who provide a response of Korean American.

Vietnamese
Includes people who indicate their race as "Vietnamese" or who provide a response of Vietnamese American.

Cambodian
Includes people who provide a response such as Cambodian or Cambodia.

Hmong
Includes people who provide a response such as Hmong, Laohmong, or Mong.

Laotian
Includes people who provide a response such as Laotian, Laos, or Lao.

Includes people who provide a response such as Thai, Thailand, or Siamese.

Other Asian
Includes people who provide a response of Bangladeshi; Bhutanese; Burmese; Indochinese; Indonesian; Iwo Jiman; Madagascar; Malaysian; Maldivian; Nepalese; Okinawan; Pakistani; Singaporean; Sri Lankan; or Other Asian, specified and Other Asian, not specified.

Native Hawaiian or Other Pacific Islander
A person having origins in any of the original peoples of Hawaii, Guam, Samoa, or other Pacific Islands. It includes people who indicate their race as "Native Hawaiian," "Guamanian or Chamorro," "Samoan," and "Other Pacific Islander."

Native Hawaiian
Includes people who indicate their race as "Native Hawaiian" or who identify themselves as "Part Hawaiian" or "Hawaiian."

Guamanian or Chamorro
Includes people who indicate their race as such, including written entries of Chamorro or Guam.

Samoan
Includes people who indicate their race as "Samoan" or who identify themselves as American Samoan or Western Samoan.

Other Pacific Islander
Includes people who provide a write-in response of a Pacific Islander group, such as Carolinian, Chuukese (Trukese), Fijian, Kosraean, Melanesian, Micronesian, Northern Mariana Islander, Palauan, Papua New Guinean, Pohnpeian, Polynesian, Solomon Islander, Tahitian, Tokelauan, Tongan, Yapese, or Pacific Islander, not specified.

Some other race
Includes all other responses not included in the "White," "Black or African American," "American Indian or Alaska Native," "Asian," and "Native Hawaiian or Other Pacific Islander" race categories described above. Respondents providing write-in entries such as multiracial, mixed, interracial, or a Hispanic/Latino group (for example, Mexican, Puerto Rican, or Cuban) in the "Some other race" write-in space are included in this category.

Two or more races
People may have chosen to provide two or more races either by checking two or more race response check boxes, by providing multiple write-in responses, or by some combination of check boxes and write-in responses. The race response categories shown on the questionnaire are collapsed into the five minimum race groups identified by the OMB, and the Census Bureau "Some other race" category. For data product purposes, "Two or more races" refers to combinations of two or more of the following race categories:
  1. White
  2. Black or African American
  3. American Indian and Alaska Native
  4. Asian
  5. Native Hawaiian and Other Pacific Islander
  6. Some other race
There are 57 possible combinations (see Figure B-1) involving the race categories shown above. Thus, according to this approach, a response of "White" and "Asian" was tallied as two or more races, while a response of "Japanese" and "Chinese" was not because "Japanese" and "Chinese" are both Asian responses. Tabulations of responses involving reporting of two or more races within the American Indian and Alaska Native, Asian, or Native Hawaiian and Other Pacific Islander categories are available in other data products.

Given the many possible ways of displaying data on two or more races, data products will provide varying levels of detail. The most common presentation shows a single line indicating "Two or more races." Some data products provide totals of all 57 possible combinations of two or more races, as well as subtotals of people reporting a specific number of races, such as people reporting two races, people reporting three races, and so on.

In other presentations on race, data are shown for the total number of people who reported one of the six categories alone or in combination with one or more other race categories. For example, the category "Asian alone or in combination with one or more other races" includes people who reported Asian alone and people who reported Asian in combination with White, Black or African American, Native Hawaiian and Other Pacific Islander, and Some other race. This number, therefore, represents the maximum number of people who reported as Asian in the question on race. When this data presentation is used, the individual race categories will add to more than the total population because people may be included in more than one category.

Coding of write-in entries
During 100-percent processing of Census 2000 questionnaires, subject-matter specialists reviewed and coded written entries from four response categories on the race item American Indian or Alaska Native, Other Asian, Other Pacific Islander, and Some other race. The Other Asian and Other Pacific Islander response categories shared the same write-in area on the questionnaire.

Comparability
The data on race in Census 2000 are not directly comparable to those collected in previous censuses. The October 1997 revised standards issued by the OMB led to changes in the question on race for Census 2000. The Census 2000 Dress Rehearsal data were the first to reflect these changes. First, respondents were allowed to select more than one category for race. Second, the sequence of the questions on race and Hispanic origin changed. In 1990, the question on race (Item 4) preceded the question on Hispanic origin (Item 7) with two intervening questions. For Census 2000, the question on race immediately follows the question on Hispanic origin. Third, there were terminology changes to the response categories, such as spelling out "American" instead of "Amer." for the American Indian or Alaska Native category; and adding "Native" to the Hawaiian response category. The 1990 category "Other race" was renamed "Some other race."

Other differences that may affect comparability involve the individual categories on the Census 2000 questionnaire. The 1990 category, "Asian and Pacific Islander" was separated into two categories, "Asian" and "Native Hawaiian and Other Pacific Islander." Accordingly, on the Census 2000 questionnaire, there were seven Asian categories and four Native Hawaiian and Other Pacific Islander categories. The two residual categories, "Other Asian" and "Other Pacific Islander," replaced the 1990 single category "Other API." The 1990 categories "American Indian," "Eskimo," and "Aleut" were combined into "American Indian and Alaska Native." American Indians and Alaska Natives can report one or more tribes.

As in 1990, people who reported a Hispanic or Latino ethnicity in the question on race and did not mark a specific race category were classified in the "Some other race" category ("Other race" in 1990). They commonly provided a write-in entry such as Mexican, Puerto Rican, or Latino. In the 1970 census, most of these responses were included in the "White" category. In addition, some ethnic entries that in 1990 may have been coded as White or Black are now shown in the "Some other race group."

For Puerto Rico, separate questions on race and Hispanic origin were included on their Census 2000 questionnaire, identical to the questions used in the United States. The 1950 census was the last census to include these questions on the Puerto Rico questionnaire.

Census 2000 included an automated review, computer edit, and coding operation on a 100- percent basis for the write-in responses to the race question, similar to that used in the 1990 census. Write-in responses such as Laotian or Thai, and Guamanian or Tongan were reviewed, coded, and tabulated as "Other Asian" and "Other Pacific Islander," respectively, in the census. All tribal entries were coded as either American Indian or as Alaska Native.
For more information on race, please telephone 301-457-2402.

Figure B-1. Two or More Races (57 Possible Specified Combinations)

  1. White; Black or African American

  2. White; American Indian and Alaska Native

  3. White; Asian

  4. White; Native Hawaiian and Other Pacific Islander

  5. White; Some other race

  6. Black; American Indian and Alaska Native

  7. Black; Asian

  8. Black; Native Hawaiian and Other Pacific Islander

  9. Black; Some other race

  10. American Indian and Alaska Native; Asian

  11. American Indian and Alaska Native; Native Hawaiian or Other Pacific Islander

  12. American Indian and Alaska Native; Some other race

  13. Asian; Native Hawaiian and Other Pacific Islander

  14. Asian; Some other race

  15. Native Hawaiian and Other Pacific Islander; Some other race

  16. White; Black; American Indian and Alaska Native

  17. White; Black; Asian

  18. White; Black; Native Hawaiian and Other Pacific Islander

  19. White; Black; Some other race

  20. White; American Indian and Alaska Native; Asian

  21. White; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander

  22. White; American Indian and Alaska Native; Some other race

  23. White; Asian; Native Hawaiian and Other Pacific Islander

  24. White; Asian; Some other race

  25. White; Native Hawaiian and Other Pacific Islander; Some other race

  26. Black; American Indian and Alaska Native; Asian

  27. Black; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander

  28. Black; American Indian and Alaska Native; Some other race

  29. Black; Asian; Native Hawaiian and Other Pacific Islander

  30. Black; Asian; Some other race

  31. Black; Native Hawaiian and Other Pacific Islander; Some other race

  32. American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander

  33. American Indian and Alaska Native; Asian; Some other race

  34. American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race

  35. Asian; Native Hawaiian and Other Pacific Islander; Some other race

  36. White; Black; American Indian and Alaska Native; Asian

  37. White; Black; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander

  38. White; Black; American Indian and Alaska Native; Some other race

  39. White; Black; Asian; Native Hawaiian and Other Pacific Islander

  40. White; Black; Asian; Some other race

  41. White; Black; Native Hawaiian and Other Pacific Islander; Some other race

  42. White; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific mIslander

  43. White; American Indian and Alaska Native; Asian; Some other race

  44. White; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race

  45. White; Asian; Native Hawaiian and Other Pacific Islander; Some other race

  46. Black; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander

  47. Black; American Indian and Alaska Native; Asian; Some other race

  48. Black; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race

  49. Black; Asian; Native Hawaiian and Other Pacific Islander; Some other race

  50. American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race

  51. White; Black; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander

  52. White; Black; American Indian and Alaska Native; Asian; Some other race

  53. White; Black; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race

  54. White; Black; Asian; Native Hawaiian and Other Pacific Islander; Some other race

  55. White; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific mIslander; Some other race

  56. Black; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race

  57. White; Black; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race



The data on sex were derived from answers to a question that was asked of all people. Individuals were asked to mark either "male" or "female" to indicate their sex. For most cases in which sex was not reported, it was determined by the appropriate entry from the persons given (i.e., first) name and household relationship. Otherwise, sex was imputed according to the relationship to the householder and the age of the person. (For more information on imputation, see "Accuracy of the Data.")

Sex ratio
A measure derived by dividing the total number of males by the total number of females and multiplying by 100.

Comparability
A question on the sex of individuals has been asked of the total population in every census.
For more information on sex, please telephone 301-457-2378.

Housing Characteristics
Living Quarters
Living quarters are either housing units or group quarters. (For more information, see the discussion of "Group Quarters" under "Population Characteristics.") Living quarters are usually found in structures intended for residential use, but also may be found in structures intended for nonresidential use as well as in places such as tents, vans, emergency and transition shelters, dormitories, and barracks.

Housing unit
A housing unit may be a house, an apartment, a mobile home, a group of rooms, or a single room that is occupied (or, if vacant, is intended for occupancy) as separate living quarters. Separate living quarters are those in which the occupants live separately from any other individuals in the building and that have direct access from outside the building or through a common hall. For vacant units, the criteria of separateness and direct access are applied to the intended occupants whenever possible. If that information cannot be obtained, the criteria are applied to the previous occupants.

Both occupied and vacant housing units are included in the housing unit inventory. Boats, recreational vehicles (RVs), vans, tents, and the like are housing units only if they are occupied as someones usual place of residence. Vacant mobile homes are included provided they are intended for occupancy on the site where they stand. Vacant mobile homes on dealers lots, at the factory, or in storage yards are excluded from the housing inventory. Also excluded from the housing inventory are quarters being used entirely for nonresidential purposes, such as a store or an office, or quarters used for the storage of business supplies or inventory, machinery, or agricultural products.

Occupied housing unit
A housing unit is occupied if it is the usual place of residence of the person or group of people living in it at the time of enumeration or if the occupants are only temporarily absent; that is, away on vacation or business. The occupants may be a single family, one person living alone, two or more families living together, or any other group of related or unrelated people who share living quarters.

Occupied rooms or suites of rooms in hotels, motels, and similar places are classified as housing units only when occupied by permanent residents; that is, people who consider the hotel as their usual place of residence or who have no usual place of residence elsewhere.

If any of the occupants in rooming or boarding houses, congregate housing, or continuing care facilities live separately from others in the building and have direct access, their quarters are classified as separate housing units.

The living quarters occupied by staff personnel within any group quarters are separate housing units if they satisfy the housing unit criteria of separateness and direct access; otherwise, they are considered group quarters.

Vacant housing unit
A housing unit is vacant if no one is living in it at the time of enumeration, unless its occupants are only temporarily absent. Units temporarily occupied at the time of enumeration entirely by people who have a usual residence elsewhere are classified as vacant.

New units not yet occupied are classified as vacant housing units if construction has reached a point where all exterior windows and doors are installed and final usable floors are in place.

Vacant units are excluded from the housing inventory if they are open to the elements; that is, the roof, walls, windows, and/or doors no longer protect the interior from the elements. Also excluded are vacant units with a sign that they are condemned or they are to be demolished.

Comparability
The first Census of Housing in 1940 established the "dwelling unit" concept. Although the term became "housing unit" and the definition was modified slightly in succeeding censuses, the housing unit definition remained essentially comparable between 1940 and 1990. Since 1990, two changes were made to the housing unit definition.

The first change eliminated the concept of "eating separately." The elimination of the eating criterion is more in keeping with the United Nations definition of a housing unit that stresses the entire concept of separateness rather than the specific "eating" element. Although we previously included the "eating separately" criterion in the definition of a housing unit, data were not collected that allowed us to distinguish whether the occupants ate separately from any other people in the building. (Questions that asked households about their eating arrangements have not been included in the census after 1970.) Therefore, the current definition better reflects the information that is used in the determination of a housing unit.

The second change for Census 2000 eliminated the "number of nonrelatives" criterion; that is, "9 or more people unrelated to the householder" which caused a conversion of housing units to group quarters. This change was prompted by the following considerations: (1) there were relatively few such conversions made as a result of this rule in 1990; (2) household relationship and housing data were lost by converting these units to group quarters; and (3) there was no empirical support for establishing a particular number of nonrelatives as a threshold for these conversions.

In 1960, 1970, and 1980, vacant rooms in hotels, motels, and other similar places where 75 percent or more of the accommodations were occupied by permanent residents were counted as part of the housing inventory. We intended to classify these vacant units as housing units in the 1990 census. However, an evaluation of the data collection procedures prior to the 1990 census indicated that the concept of permanency was a difficult and confusing procedure for enumerators to apply correctly. Consequently, in the 1990 census, vacant rooms in hotels, motels, and similar places were not counted as housing units. In Census 2000, we continued the procedure adopted in 1990.
For more information on housing units, please telephone 301-457-3191.

Average Household Size of Owner-Occupied Unit
A measure obtained by dividing the number of people living in owner-occupied housing units by the number of owner-occupied housing units.
For more information on average population per owner-occupied unit, please telephone 301-457-3191.

Average Household Size of Renter-Occupied Unit
A measure obtained by dividing the number of people living in renter-occupied housing units by the number of renter-occupied housing units.
For more information on average population per renter-occupied unit, please telephone 301-457-3191.

Tenure
Tenure was asked at all occupied housing units. All occupied housing units are classified as either owner occupied or renter occupied.

Owner occupied
A housing unit is owner occupied if the owner or co-owner lives in the unit even if it is mortgaged or not fully paid for. The owner or co-owner must live in the unit and usually is Person 1 on the questionnaire. The unit is "Owned by you or someone in this household with a mortgage or loan" if it is being purchased with a mortgage or some other debt arrangement, such as a deed of trust, trust deed, contract to purchase, land contract, or purchase agreement. The unit is also considered owned with a mortgage if it is built on leased land and there is a mortgage on the unit.

A housing unit is "Owned by you or someone in this household free and clear (without a mortgage or loan)" if there is no mortgage or other similar debt on the house, apartment, or mobile home including units built on leased land if the unit is owned outright without a mortgage. Although owner-occupied units are divided between mortgaged and owned free and clear on the questionnaire, census data products containing 100-percent data show only total owner-occupied counts. More extensive mortgage information is collected on the long-form questionnaire.

Renter occupied
All occupied housing units that are not owner occupied, whether they are rented for cash rent or occupied without payment of cash rent, are classified as renter occupied. "No cash rent" units are separately identified in the rent tabulations. Such units are generally provided free by friends or relatives or in exchange for services, such as resident manager, caretaker, minister, or tenant farmer. Housing units on military bases also are classified in the "No cash rent" category. "Rented for cash rent" includes units in continuing care, sometimes called life care arrangements. These arrangements usually involve a contract between one or more individuals and a service provider guaranteeing the individual shelter, usually a house or apartment, and services, such as meals or transportation to shopping or recreation.

Comparability
Data on tenure have been collected since 1890. In 1990, the response categories were expanded to allow the respondent to report whether the unit was owned with a mortgage or loan, or free and clear (without a mortgage). The distinction between units owned with a mortgage and units owned free and clear was added in 1990 to improve the count of owner-occupied units. Research after the 1980 census indicated some respondents did not consider their units owned if they had a mortgage. In Census 2000, we continued with the same tenure categories used in the 1990 census.
For more information on tenure, please telephone 301-457-3191.

Vacancy Status
The data on vacancy status were obtained from Enumerator Questionnaire, Item C. Vacancy status and other characteristics of vacant units were determined by census enumerators obtaining information from landlords, owners, neighbors, rental agents, and others. Vacant units are subdivided according to their housing market classification as follows:

For rent
These are vacant units offered "for rent" and vacant units offered either "for rent or for sale."

For sale only
These are vacant units offered "for sale only," including units in cooperatives and condominium projects if the individual units are offered "for sale only."

Rented or sold, not occupied
If any money rent has been paid or agreed upon but the new renter has not moved in as of the date of enumeration, or if the unit has recently been sold but the new owner has not yet moved in, the vacant unit is classified as "rented or sold, not occupied."

For seasonal, recreational, or occasional use
These are vacant units used or intended for use only in certain seasons, for weekends, or other occasional use throughout the year. Seasonal units include those used for summer or winter sports or recreation, such as beach cottages and hunting cabins. Seasonal units also may include quarters for such workers as herders and loggers. Interval ownership units, sometimes called shared-ownership or time-sharing condominiums, also are included in this category.

For migrant workers
These include vacant units intended for occupancy by migratory workers employed in farm work during the crop season. (Work in a cannery, a freezer plant, or a foodprocessing plant is not farm work.)

Other vacant
If a vacant unit does not fall into any of the classifications specified above, it is classified as "other vacant." For example, this category includes units held for occupancy by a caretaker or janitor, and units held for personal reasons of the owner.

Available housing
Available housing units are vacant units that are for sale only or for rent.

Available housing vacancy rate
The proportion of the housing inventory that is available for sale only or for rent. It is computed by dividing the number of available units by the sum of the occupied units and the number of available units, and then multiplying by 100.

Home owner vacancy rate
The proportion of the homeowner housing inventory that is vacant for sale. It is computed by dividing the number of vacant units for sale only by the sum of the owner-occupied units and vacant units that are for sale only, and then multiplying by 100.

Rental vacancy rate
The proportion of the rental inventory that is vacant for rent. It is computed by dividing the number of vacant units for rent by the sum of the renter-occupied units and the number of vacant units for rent, and then multiplying by 100.

Comparability
Data on vacancy status have been collected since 1940. Since 1990, we have used the category "For seasonal, recreational, or occasional use." In earlier censuses, separate categories were used to collect data on these types of vacant units. Also, in 1970 and 1980, housing characteristics generally were presented only for year-round units. Beginning in 1990 and continuing into Census 2000, housing characteristics are shown for all housing units.
For more information on vacancy status, please telephone 301-457-3191.

Derived Measures
Census data products include various derived measures, such as medians, means, and percentages, as well as certain rates and ratios. Derived measures that round to less than 0.1 are not shown but indicated as zero.

Average
See mean.

Interpolation
Interpolation frequently is used in calculating medians based on interval data and in approximating standard errors from tables. Linear interpolation is used to estimate values of a function between two known values. This is the form of interpolation used to calculate median age.

This measure represents an arithmetic average of a set of values. It is derived by dividing the sum (or aggregate) of a group of numerical items by the total number of items in that group. For example, average family size is obtained by dividing the number of people in families by the total number of families (or family householders). (Additional information on means and aggregates is included in the separate explanations of many of the population and housing subjects.)

Median
This measure represents the middle value (if n is odd) or the average of the two middle values (if n is even) in an ordered list of n data values. The median divides the total frequency distribution into two equal parts: one-half of the cases fall below the median and one-half of the cases exceed the median. Each median is calculated using a standard distribution. (See also "Interpolation.")

For data products in publication or display table format, if the median falls within the upper interval of an open-ended distribution, the median is shown as the initial value of the interval followed by a plus sign (+), or if within the lower interval, the median is shown as the upper value of the category followed by a minus sign (-).
For products on CD-ROM and products that can be downloaded by a user as data files (no text, just numbers), if the median falls within the upper or lower interval, it is set to a specified value, but with no plus or minus symbol.

Percentage
This measure is calculated by taking the number of items in a group possessing a characteristic of interest and dividing by the total number of items in that group, and then multiplying by 100.

This is a measure of occurrences in a given period of time divided by the possible number of occurrences during that period. Rates are sometimes presented as percentages.

Rounding
The computation of means and, especially, medians to a fixed number of decimal places can introduce nonsampling error-computational rounding. This will only be noticable when each of two situations obtains: (1) the value being computed is very near (to less than one part in a billion) to or is exactly halfway between two representable numbers (e.g., a value of 35.85 when rounding to one decimal place), and (2) the same result has been computed in two separate data products (e.g., Summary File 1 State files or Advanced file as compared to the Final National file.

Thus, if for a particular datum one data product were to report 35.8 and a different data product reported 35.9, this is because the value, if computed exactly from the same sampled and edited data would lie somewhere between 35.8499999999 and 35.8500000001.