to the public in order to protect the confidentiality of individual responses. For the long-form records, there are the added steps of coding such variables as occupation and industry and weighting the records to short-form control totals on several dimensions.
The 1990 census data processing system was more decentralized than in 2000 and made more use of clerical editing (see National Research Council, 1995:App.B). There were 7 processing offices and 559 district offices. Mailback questionnaires in district offices in hard-to-enumerate areas in central cities went directly to a processing office for check-in and data capture. Mailback questionnaires in other district offices and all enumerator-obtained returns went first to the district office for check-in and editing.
Mailback questionnaires sent to processing offices were checked in by scanning bar codes. The data were then captured by using the Census Bureau’s Film Optical Sensing Device for Input to Computers (FOSDIC), first developed for the 1960 census (Salvo, 2000). The computerized records were put through edit checks to identify households that had not provided complete data or would otherwise need telephone or personal visit follow-up (see “Field Follow-Up,” above). Once any further data had been received from the field, computerized editing, allocation, and imputation routines were used to fill in remaining missing or inconsistent data
Mailback questionnaires sent to district offices were checked in by scanning bar codes and then reviewed by clerks to identify cases that required follow-up. After completion of follow-up, the questionnaires were sent to the processing offices for data capture and computerized editing and imputation.
Another step in data processing included the search/match operation, in which forms received from various activities were checked against completed questionnaires for the same address to determine which people should be added to the household roster and which were duplicates. This operation was carried out for “Were You Counted” forms, parolee/probationer forms, and for people who sent in a questionnaire from one location with an indication that their usual home was elsewhere. Such people might have two homes, such as people who spend the winter in a southern state and the summer in a northern state. There was no way on the 2000 form to indicate usual home elsewhere.
At the conclusion of data processing in 1990, about 1.9 million people had their information imputed (substituted) from data for another person. Substituted people accounted for 0.8 percent of the household population in 1990, compared with 2.1 percent in 2000. Obtaining comparable rates of imputations of characteristics for people with partial data is difficult. It appears that rates of editing and imputation for short-form items were similar in 1990 and 2000— somewhat lower for some items and somewhat higher for other items.