the 1990 census) was used. However, there was no precensus local review program for the ACF in these areas.
The 2000 census, like the 1980 and 1990 censuses, was conducted primarily by delivering questionnaires to households and asking them to mail back a completed form. Procedures differed somewhat depending on such factors as type of addresses in an area and accessibility; in all, there were nine types of enumeration areas. Box C.2 provides brief descriptions of the nine types in 2000.
The two largest types of enumeration areas were: (1) mailout/ mailback, covering almost 82 percent of the population, in which Postal Service carriers delivered questionnaires, and (2) update/ leave/mailback (usually termed update/leave), covering almost 17 percent of the population, in which Census Bureau field staff delivered questionnaires and updated the MAF at the same time. These two types, together with small numbers of addresses in areas (6), (7), and (9), comprised the mailback universe, covering about 99 percent of the household population (calculated from Baumgardner et al., 2001). The remaining 1 percent of the household population was counted by census enumerators (see areas (3), (4), (5), and (8) in Box C.2). Separate enumeration procedures were used for such special populations as homeless people, residents of group quarters, and transients (see Citro, 2000c).
Approaches to boost mail response were to redesign the questionnaire and mailing package, adapt enumeration procedures to special situations (the reason for having nine types of enumeration areas), and allow multiple modes for response. Advertising and outreach efforts were also expanded from 1990 (see Section C.4).
The final mail response rate in 2000 (67 percent) was slightly higher than the rate in 1990 (65 percent); it was also considerably higher than the rate that was budgeted (61 percent), which reduced the burden of field follow-up. The mail return rate in 2000 (78 percent) was higher than the rate in 1990 (75 percent). This rate is a more refined measure of public cooperation than the mail response rate, which includes vacant and nonresidential addresses in the denominator in addition to occupied housing units (see Chapter 4, Box 4.1).