reinterview by telephone. About 2.3 million cases were in the telephone follow-up workload, including: returns that reported a higher total count of household members than the number of members for which individual information (e.g., age, race, sex) was provided; returns that did not report a household count and provided information for exactly six people (the limit of the space provided on the questionnaire); returns that reported household counts of seven people or more; and returns of four or more people that contained nonrelatives of the household head. The purpose of the operation was to reduce undercounting of people in large households and nonfamily households. (Telephone follow-up was also used in the 1990 census, but, unlike 2000, the 1990 operation addressed missing characteristics as well as coverage problems and included a field follow-up effort when telephone follow-up was not successful.)
Unduplication of households and people: Two major, computer-based unduplication operations were carried out subsequent to field follow-up. One operation was the special effort in summer 2000 to reduce duplication of housing unit addresses in the MAF (see “Unduplication and Late Additions,” above). The other operation, which was planned from the outset, used the primary selection algorithm (PSA) to unduplicate multiple returns for the same address.
The purpose of the PSA was to determine which households and people to include in the census when more than one questionnaire was returned with the same census address identification number. Such duplication could occur, for example, when a respondent mailed back a census form after the cutoff date for determining the NRFU workload and the enumerator then obtained a second form from the household. In all, 9 percent of census housing units had two returns and 0.4 percent had three or more returns. In most instances, the PSA discarded duplicate household returns or extra vacant returns; less often, the PSA found additional people to assign to a basic return or identified more than one household at an address.
Editing and imputation: It is standard census practice to use editing techniques to reconcile inconsistent or anomalous answers for a person or household and to use imputation routines to provide values for missing responses. In 2000, all editing and imputation were computer-based; there was no clerical editing of the questionnaires as in 1990 and past censuses. In instances when it was not possible to perform an edit that used other information for the same person or household, imputation was performed with “hot deck” methods that made use of information for other, similar people and households in the immediate neighborhood (see Box A-3 in Appendix A).