The Sixteenth Census of the United States covered the continental United States, Alaska, American Samoa, Guam, Hawaii, the Panama Canal Zone, Puerto Rico, the Virgin Islands of the United States, the military and consular services abroad, and naval services abroad or in American waters, but not at a fixed station.¹ Persons in the military services were enumerated as residents of the states, counties, and minor civil divisions in which their posts of duty were located (members of their families were enumerated at the place in which they resided). The crews of American merchant marine vessels were enumerated as part of the population of the port from which the vessel operated.

No apportionment had been done after the 1920 Census—the 1910 apportionment remained in effect. Consequently, the 1929 act included provisions that, for the 1930 and subsequent censuses, (unless the Congress, within a specified time enacted legislation providing for apportionment on a different basis) the apportionment should automatically be made by the method last used. In accordance with this act, a report was submitted by the President to the Congress on December 4, 1930, showing the apportionment computations both by the method of major fractions (which was used in 1910) and by the method of equal proportions. In 1931, in the absence of additional legislation, the method of major fractions was automatically followed.²

In the application of this method, the Representatives are so assigned that the average population per Representative has the least possible variation as between one state and any other. As a result, California gained three Representatives between 1930 and 1940 and six other states—Arizona, Florida, New Mexico, North Carolina, Oregon, and Tennessee—each gained one. To balance these gains (since the number of Representatives in the House was not changed), nine states lost one Representative each—Illinois, Indiana, Iowa, Kansas, Massachusetts, Nebraska, Ohio, Oklahoma, and Pennsylvania.

Four notable changes were made to the 1940 Census, including the addition of the housing schedule, the sampling procedure (both discussed in further detail below), the incorporation of the questions on employment and unemployment on to the general population³ schedule, and inquiries into migration.⁴

On August 11, 1939, a national census of housing was approved by the Congress, “to provide information concerning the number, characteristics (including utilities and equipment), and geographic distribution of dwelling structures and dwelling units in the United States. The Director of the Census shall take a census of housing in each state, the District of Columbia, Hawaii, Puerto Rico, the Virgin Islands, and Alaska, in the year 1940 in conjunction with, and at the same time, and as part of the population inquiry of the sixteenth decennial census.”

The housing inquiries were collected via a separate census, partly because they were added by legislation late in the census planning, and partly because the nature of the questions so differed from those of the census of population.

The information collected by the two schedules was collected, however, by the same enumerator, at the same time as those for the population schedule.

Use of Sampling in the 1940 Census. The 1940 sample was a representative cross-section of the entire population. Tabulations made from the sample would be as nearly as possible the same as if information concerning every person had been obtained. The sample enlarged the scope of the census and facilitated tabulations in the following ways:

• Since the supplementary questions were asked only 1/20 th (5-percents ample) as often as they would have in a complete census, the speed of field work was increased and carried out at a reduced cost, thus making it possible to carry more questions on the schedule.
• Tabulations based on the sample could be completed months ahead of the regular tabulations prepared from the general population—an especially important feature in times of national emergency and for obtaining quick preliminary counts of the distribution of the labor force by area, sex, age, etc.
• The reduced cost of sample tabulations permitted the publication of data that otherwise would not be possible.
• Sample cards could be stored for subsequent tabulations not feasible for the entire population as the need arose.
• Sampling helped to adapt the census to newly developed needs, and to maintain continuity from one census to another.

Participants were selected for the sample by designating 2 of the 40 lines on each side of the schedule as sample lines and instructing the enumerators to ask the supplementary questions for each person whose name happened to fall on these lines. This method resulted in a 5-percent sample of all the lines in each geographic area. The actual percentage of persons drawn from the sample from any district would vary by chance, depending on how the names happened to “lineup” as the enumerators proceeded with their enumeration.

¹ Again, the Philippine Islands were not included in the United States decennial census. The commonwealth of the Philippines conducted a census in 1939. The statistics from this census were then included in the data from the 1940 Census.

² In 1941, this law was amended to the effect that apportionment based on the1940 and subsequent censuses should be made by the method of equal proportions.

³ These inquiries had been made by special Census of Unemployment in 1930 (See 1930 Unemployment Census).

⁴ A question was added asking, for each person 5 years old and above, the residence on April 1, 1935. These data were coded and compared to the place of residence in 1940, thus providing, for the first time, statistics on population movement.