When planning for the 1970 census, the need for an accurate count of the population was even greater than in the past because of the increasing tendency for governmental bodies to use population as a basis for distributing funds, and the more general awareness by local government officials and others of the potential effects of census undercounts.

Throughout the 1960s, researchers had reported that the population was increasingly resistant to the census. Studies had shown more alienation and distrust of government, and there appeared to be more organized attempts to protest the census. Furthermore, undercounts following the 1950 and 1960 censuses were blamed upon the enumerators’ failure to follow instructions. Hence, stress was placed on simplified procedures, training, and quality control. Analysis of the results of the 1960 evaluation program and studies performed in the 1950s and 1960s indicated that the reasons for the under counts were more complex. In particular, a substantial part of the undercount appeared to be due to either deliberate attempts by some segments of the population to be omitted from the census or the fact that they did not fit into any households by the “conventional rules” of residence. Even where the undercount was due to complete households being missed, the causes were frequently such that additional enumerator training produced only marginal gains.

This analysis led to a two-phase approach to coverage for the 1970 census. The first phase was the use of a basic census methodology that permitted knowledgeable outside sources to have an offer in put into the list of housing units established by the census, and provided for automatic checks that enumerators actually completed a questionnaire for all known units.¹ This was done in areas containing about 60 percent of the population through the creation of an address register independent of the enumeration phase, correction and updating of the register by U.S. Post Office employees familiar with their routes, and checks by Census Bureau employees to ensure that all housing units on the address register were accounted for when enumerators had completed their assignments.

A self-enumeration questionnaire was used in 1970 (as in 1960 for 60 percent of the population). Such questionnaires were believed to provide better reporting within households, because they provided respondents uniform census definitions and rules to follow for unusual household residence situations. In the areas containing the remaining 40 percent of the population, more conventional listing procedures were followed, but with self-enumeration features.

The second phase of the 1970 enumeration was to superimpose on the regular census procedures projects specifically designed to increase coverage. Prior to 1970, studies of the effectiveness of a variety of devices for improving coverage were made, generally as part of large-scale tests conducted during the 1960s, which resulted in several coverage improvement initiatives.

The 1970 coverage improvement program included measures to improve coverage by (1) developing a more favorable public view of the census; (2) increasing the public’s understanding of the importance of the census and its confidentiality; and (3) improving the enumerators’ performance in hard-to-enumerate areas through intensive training and supervision. The specific changes made included—

• A sharp reduction in the number of questions to be asked of households—the number of inquiries on the questionnaire intended for 3 million households had been reduced from 66 to 23.
• Questions on the adequacy of kitchen and bathroom facilities were reworded to remove any implication that the federal government was trying to ascertain with whom these were shared.
• The Secretary of Commerce increased his supervision of the census and retained independent experts as census advisors.
• A letter accompanied the census questionnaire that explained the need for data requested and emphasized the confidentiality of responses.²

Census questionnaires with instruction sheets were delivered by the U.S. Post Office to every household several days prior to “Census Day”—April 1, 1970. In areas with comparatively large populations of Spanish-speaking households, a Spanish-language version of the instruction sheet also was enclosed. Households either received a short-form questionnaire, which contained questions asked of 100 percent of the population (80 percent of the population received this form), or a long-form questionnaire, sent to 20 percent of the population, containing questions asked of 15 and 5 percent of the population.

In larger metropolitan areas and some adjacent counties (approximately 60 percent of the United States’ population), households were asked to complete and return the questionnaire by mail on April 1, 1970 (resulting in an 87 percent mail back response rate), which was then reviewed by an enumerator or census clerk. Telephone or personal follow-up was made to complete or correct missing, incomplete, or inconsistent questionnaires. For the remaining 40 percent of the United States’ population, instructions asked that the householder complete the form and hold it for pickup by an enumerator.

¹ Throughout the census history, a small percentage of enumerators completed questionnaires by “curb stoning.” Curb stoning meant the enumerator completed questionnaires for an individual or multiple households from the curb, without actually conducting an interview or checking the accuracy of their “guesses.” This practice was motivated, in part, by the requirement to meet quotas or payment for work done on a “piece-of-work” basis.

² United States Department of Commerce News, April 18, 1969. P.1.