Population coverage. The figures in this report for March 1986 and March 1987 are sample survey data and relate to the noninstitutional population of the 50 States and the District of Columbia. Members of the Armed Forces living off post or with their families on post are included; all other members of the Armed Forces are excluded. The March 1986 survey included 1,090,000 members of the Armed Forces, and the March 1987 survey included 896,000 members.

Population figures shown for States and SMSA's are based on weighted results of the Current Population Survey and have not been adjusted to independent Census Bureau estimates.

The estimation procedure used for this survey involves the inflation of the weighted sample results to independent estimates of the civilian noninstitutional population of the United States by age, race, and sex. These independent estimates are based on civilian noninstitutional population counts from the decennial censuses and are updated with statistics on births, deaths, immigration, and emigration and statistics on the strength of the Armed Forces. Data published in this series for 1972 through 1979 were based on independent population estimates derived by updating the 1970 decennial census counts. Starting with the data collected in March 1980 Current Population Survey (CPS), independent estimates were based on civilian noninstitutional population controls for age, race, and sex established by the 1980 decennial cen

sus.

The April 1980 census population count differed somewhat from the independent estimates for April 1980 derived by updating 1970 census population figures. The April 1980 census count of the civilian noninstitutional population was 222,420,441, compared with the 1970 census based figure of 217,400,244 used for the CPS. Basically, this difference had little impact on summary or proportional measures, such as medians and percent distributions; however, use of the new controls could have significant effect on the absolute numbers.

Undocumented immigrants. The 1980 census counted about 2 million undocumented immigrants according to Census Bureau estimates. Beginning in January 1986, the independent population controls included an allowance for growth in the undocumented population for every year since 1980. This methodological

change was partially offset by another change that increased the allowance for emigration of legal residents. Data shown for Current Population Surveys with controls based on pre-1986 methods have not been revised to take into account these methodological changes. Consequently, direct comparisons of CPS figures for months before January 1986 with later months will not be consistent. Series P-25, No. 985, reviews the postcensal population estimates methodology currently in use.

Age. The age classification is based on the age of the person at his last birthday.

Race. The population is divided into three groups on the basis of race: White, Black, and "other races." The last category includes Indians, Japanese, Chinese, and any other race except White and Black. In this report, "other races" is not shown separately.

Spanish origin. Information on origin or descent was obtained by asking "What is (this person's) origin or descent?" Responses generally refer to a person's perceived national or ethnic lineage and do not necessarily indicate the country of birth of himself or his parents.

Persons of Spanish origin are persons who reported themselves as Mexican American, Chicano, Mexican, Mexicano, Puerto Rican, Cuban, Central or South American, or other Spanish origin. However, all persons who reported themselves as Mexican American, Chicano, Mexican, or Mexicano were combined into the one category: Mexican. Persons of Spanish origin may be of any race.

Years of school completed. Data on years of school completed in this report were derived from the combination of answers to two questions: (a) “What is the highest grade of school he has ever attended?" and (b) "Did he finish this grade?"

The questions on educational attainment apply only to progress in "regular" schools. Such schools include graded public, private, and parochial elementary and high schools (both junior and senior high), colleges, universities, and professional schools, whether day schools or night schools. Thus, regular schooling is that which may advance a person toward an elementary school certificate or high school diploma, or a

college, university, or professional school degree. Schooling in other than regular schools was counted only if the credits obtained were regarded as transferable to a school in the regular school system.

The median years of school completed is defined as the value which divides the population into two equal parts one-half having completed more schooling and one-half having completed less schooling than the median. This median was computed after the statistics on years of school completed had been coverted to a continuous series of numbers (e.g., completion of the first year of high school was treated as completion of the 9th year and the completion of the first year of college as completion of the 13th year). The persons completing a given school year were assumed to be distributed evenly within the interval from .0 to .9 of the year (for example, persons completing the 12th year were assumed to be distributed evenly between 12.0 and 12.9). In fact, at the time of the March survey, most of the enrolled persons had completed about three-fourths of a school year beyond the highest grade completed, whereas a large majority of persons who were not enrolled had not attended any part of a grade beyond the highest one completed. The effect of the assumption is to place the median for younger persons slightly below, and for older person's slightly above, the true median. Because of the inexact assumption as to the distribution within an interval, this median is more appropriately used for comparing groups and the same group at different dates than as an absolute measure of educational attainment.

Marital status. The marital status classification identifies four major categories: single (never married), married, widowed, and divorced. These terms refer to the marital status at the time of the enumeration.

The category "married" is further divided into "married, spouse present," "separated," and "other married, spouse absent." Only the first is shown separately in this report. A person was classified as "married, spouse present" if the husband or wife was reported as a member of the household, even though he or she may have been temporarily absent on business or on vacation, visiting, in a hospital, etc., at the time of the enumeration. Persons reported as separated included those with legal separations and other persons permanently or temporarily separated because of marital discord. The remainder includes married persons living apart because either the husband or wife was employed and living at a considerable distance from home, was serving away from home in the Armed Forces, had moved to another area, or had a different place of residence for any other reason except separation as defined above.

Household. A household consists of all the persons who occupy a housing unit. A house, an apartment or

other group of rooms, or a single room, is regarded as a housing unit when it is occupied or intended for occupancy as separate living quarters; that is, when the occupants do not live and eat with any other persons in the structure and there is direct access from the outside or through a common hall.

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 in a housing unit, or a group of unrelated persons sharing a housing unit as partners, is also counted as a household. The count of households excludes group quarters.

Householder. The householder refers to the person (or one of the persons) in whose name the housing unit is owned or rented (maintained) or, if there is no such person, any adult member, excluding roomers, boarders, or paid employees. If the house is owned or rented jointly by a married couple, the householder may be either the husband or the wife. The person designated as the householder is the "reference person" to whom the relationship of all other household members, if any, is recorded.

Prior to 1980, the husband was always considered the householder in married-couple households. The number of householders is equal to the number of households. Also, the number of family householders is equal to the number of families.

Head versus householder. Beginning with the 1980 CPS, the Bureau of the Census discontinued the use of the terms "head of household" and "head of family." Instead, the terms "householder" and "family householder" are used. Recent social changes have resulted in greater sharing of household responsibilities among the adult members and, therefore, have made the term "head" increasingly inappropriate in the analysis of household and family data. Specifically, the Census Bureau has discontinued its longtime practice of always classifying the husband as the reference person (head)when he and his wife are living together.

In this report, the term "householder" is used in the presentation of data that had previously been presented with the designation "head."

Family. A family is a group of two persons or more (one of whom is the householder) related by birth, marriage, or adoption and residing together; all such persons (including related subfamily members) are considered as members of one family.

Family household. A family household is a household maintained by a family (as defined above). The family householder is the designated householder of such a household. Prior to 1980 this person was referred to as the "family head."

Employed. Employed persons comprise those civilians who, during the survey week, were either (1) "at work"-those who did any work for pay or profit, or worked without pay for 15 hours or more on a family farm or business; or (2) "with a job but not at work"-those who did not work and were not looking for work but had a job or business from which they were temporarily absent because of vacation, illness, labor-management dispute, bad weather, or because they were taking the week off for various other reasons.

Occupation. Data on occupation are shown for the employed and relate to the job held during the survey week. Persons employed at two jobs or more were reported in the job at which they worked the greatest number of hours during the week. The major groups used here are generally the major groups used in the 1980 Census of Population, Vol. 1, Characteristics of the Population, U.S. Summary.

Metropolitan-nonmetropolitan residence. The population residing in metropolitan statistical areas (MSA's) constitutes the metropolitan population. MSA's are defined by the Office of Management and Budget for use in the presentation of statistics by agencies of the Federal Government. An MSA is a geographic area consisting of a large population nucleus, together with adjacent communities which have a high degree of economic and social integration with the nucleus. The definitions specify a boundary around each large city so as to include most of all its suburbs. Entire counties form the MSA building blocks, except in New England where cities and towns are used. The former term SMSA was changed to MSA in 1983.

An area qualifies for recognition as an MSA if (1) it includes a city of at least 50,000 population, or (2) it includes a Census Bureau-defined urbanized are of at least 50,000 with a total metropolitan population of at least 100,000 (75,000 in New England). In addition to the county containing the main city or urbanized area, an MSA may include other counties having strong commuting ties to the central county. If specific conditions are met, certain large MSA's are designated as consolidated MSA's (CMSA's) and divided into component MSA's (PMSA's).

Central cities. The largest city in each MSA is always designated a central city. There may be additional central cities if specified requirements, designed to identify places of central character within the MSA, are met. Although the largest central cities are generally included in the title of the MSA, there may be central cities that are not part of the title. The balance of the MSA outside the central city or cities often is regarded as equivalent to "suburbs."

Note to users. In July 1985, the CPS began carrying the metropolitan statistical area definitions announced by the Office of Management and Budget on June 30,

1984. Figures published from the CPS in the early 1980's and throughout most of the 1970's referred to metropolitan areas as defined on the basis of the 1970 census. Since there are important differences in the population classified as metropolitan using the 1970 and 1984 definitions, comparisons should be avoided.

The new CPS metropolitan estiamtes have consistently been higher than independent estimates of the metropolitan population prepared by the Census Bureau; the new CPS nonmetropolitan estimates have been lower than the independent estimates. For example, between July 1985 and August 1986 the magnitude of the monthly differences varied from 900,000 to 2.5 million persons, so that the proportion of the population living in metropolitan areas according to the CPS has ranged from 0.4 to 1.0 percentage points higher than the independent estimate. The difference in level between the two sets of estimates is partially attributable to the basic CPS sample design, which, because of sampling variability, includes an oversample of metropolitan households and an undersample of nonmetropolitan households. The monthly variations result from the exit and entrance of rotation groups, each with slightly different metropolitan-nonmetropolitan proportions, into the sample. The apparent overestimation of metropolitan and underestimation of nonmetropolitan population in the CPS relative to the Bureau's independent estimates should be taken into account when using the data.

Farm-nonfarm residence. The farm population refers to rural residents living on farms. The definition of a farm was changed in the mid-1970's, and the new definition was introduced into this data series beginning with the report for March 1980 and 1981.

According to the current definition, the farm population consists of all persons living in rural territory on places from which $1,000 or more of agricultural products were sold during the preceding 12 months. Rural persons in institutions, motels, and tourist camps are not classified as farm population.

The nonfarm population comprises persons living in urban areas and all rural persons not on farms. Geographic regions. The four major regions of the United States, for which data are presented in this report, represent groups of States, as follows:

Northeast: Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont.

Midwest: Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.

South: Alabama, Arkansas, Delaware, District of Columbia, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia.

West: Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming.

Symbols. A dash (-) represents zero or rounds to zero, and the symbol "B" means that the base for the

derived figure is less than 75,000. An "X" means not applicable, and "NA" means not available.

Rounding of estimates. Individual figures are rounded to the nearest thousand without being adjusted to group totals which are independently rounded. With few exceptions, percentages are based on the rounded absolute numbers.