This section relates to the population of the United States, its distribution, and its characteristics. The principal source of these data is the Decennial Census of Population, a house-to-house enumeration made by the Bureau of the Census. In accordance with a Constitutional provision for a decennial canvass of the population, the first census enumeration was made in 1790. The primary reason for the Census of Population, as set forth in the Constitution, was to provide a basis for the apportionment of Members of the House of Representatives among the several States. Until 1902, the census organization was temporary. The Bureau of the Census was then established as a permanent agency of the Government charged with responsibility for the decennial census and for compiling statistics on other subjects as needed. Currently, this Bureau supplies intercensal data based on surveys and estimates in addition to making the comprehensive decennial census enumeration.
Decennial censuses.—In accordance with Census practice dating back to 1790, each person enumerated in the 1950 Census was counted as an inhabitant of his usual place of residence or usual place of abode, that is, the place where he lives and sleeps most of the time. This place is not necessarily the same as his legal residence, voting residence, or domicile, although, in the vast majority of cases, the use of these different bases of classification would produce identical results.
Most of the data which are presented are based on complete counts. However, certain of the 1950 data are indicated as being obtained from representative samples of 20 percent or 3% percent of the population. A few tables also include 1940 data
obtained on a sample basis.
Exact agreement is not to be expected among the various samples, nor between them and the complete census count, but the sample data may be used with confidence where large numbers are involved, and may be assumed to indicate patterns and relationships where small numbers are involved. Detailed statements regarding the sampling errors are given in the original sources. In addition, experience has shown that in mass operations two tabulations of a set of punch cards are not likely to yield identical results. These differences are caused by occasional errors in the tabulation processes-machine failure, loss of punch cards, and other types.
Figures from the 1960 Census of Population, taken as of April 1, were not available when material for this section was organized and sent to the printer.
Current Population Survey.-Several tables present statistics based on the Current Population Survey, conducted monthly by the Bureau of the Census. Until May 1956, the Survey covered a sample of approximately 21,000 interviewed households spread over a sample of areas throughout the United States. Since then, the sample has been expanded to approximately 35,000 interviewed households in a larger number of areas. For a discussion of the reliability of estimates based on this sample, see Technical Note, page 203.
Population estimates.-Population estimates for dates after April 1950, which are not the result of sample surveys, are based on data from the 1950 Census; statistics of births and deaths provided by the National Office of Vital Statistics, Public Health Service; statistics of immigration and emigration reported by the Immigration and Naturalization Service, Department of Justice; and statistics on the Armed Forces provided by the Department of Defense. Estimates of State population are based on the same types of data and also make use of school statistics provided by State Departments of Education and parochial school systems throughout the country.