Unlike the original A.C.E., the revised figures were not built up from estimates for individual poststrata, but were constructed at an aggregate level for the total population and three race/ethnicity groups—non-Hispanic blacks, Hispanics, and all other.⁵ The calculations were based on an assumption that a factor for duplicates not detected by the computer matching applied equally to all race/ethnicity groups. They were based on other simplifying assumptions as well, such as that P-sample errors were not likely to affect the dual-systems estimate of the population.

Thompson et al. (2001:1) termed the revised estimates an “early approximation” of the likely effects on the estimated net undercount that might result from a corrected A.C.E. These estimates showed a reduction in the estimated net undercount of the total population in 2000 from 1.2 percent (March estimate) to 0.1 percent (October estimate) and a narrowing of the differences in net undercount rates for blacks and Hispanics compared with all others (Table 5.2).

The revised demographic analysis estimate of the total net undercount in 2000 (see Table 5.3) was virtually the same as the revised A.C.E. estimate—0.1 percent of the population. The revisions to the demographic analysis estimates incorporated additional information for estimating net immigration (particularly illegal immigration) from the 2000 census itself (the long-form sample) and the Census 2000 Supplementary Survey. It also reflected new assumptions about the extent of undercount of legal immigrants and the completeness of birth registration. Some of these changes increased the DA population estimates; others decreased them (see Robinson, 2001b).