In this chapter we first consider the role of IIs in explaining a puzzle from our initial analysis of the 2000 A.C.E. We then examine separately the characteristics of whole person imputations and people reinstated in the census too late to be included in the A.C.E. (Appendix A provides more detail on the material in this chapter.).

A PUZZLE

Our initial analysis of the 2000 A.C.E. and the 1990 PES led us to expect similar rates of net undercount for key population groups because of similarities in the estimates for each of two components of the DSE formula, namely, the match rate estimated from the P-sample and the correct enumeration rate estimated from the E-sample (see Tables 7-8 and 7-9 in Chapter 7). Yet the A.C.E. measured marked reductions in net undercount rates from 1990 levels for such groups as minorities, renters, and children and a consequent narrowing of differential undercount rates between historically less well-counted and better-counted groups.

Illuminating the Puzzle

Table 8-1 provides information from the 2000 A.C.E. and the 1990 PES that illustrates the puzzle and a large part of the solution. The first two columns of Table 8-1 show the coverage correction factors for 2000 and 1990. The coverage correction factor is the dual-systems estimate (DSE) of the population divided by the full census count, including people requiring imputation and people reinstated in the census too late for A.C.E. processing. The coverage correction factor minus one is similar to the net undercount rate (DSE minus the full census count divided by the DSE). The coverage correction factor would be used if the census data were to be adjusted for net undercount. The second two columns of Table 8-1 are the 2000 and 1990 correction ratios. The correction ratio is the estimated correct enumeration rate divided by the estimated match rate. If there were no people with insufficient information who had to be excluded from the E-sample, the correction ratio would equal the coverage correction factor. The third and last two columns of Table 8-1 are the 2000 and 1990 percentages of all people with insufficient information (IIs) in the census count, including people requiring imputation and people reinstated too late for A.C.E. processing. These people were not included in the E-sample but were added back to the census count when computing the coverage correction factors (see Chapter 6).

Looking at owners and renters for the non-Hispanic white and other races domain as an example, the correction ratios for 2000 are 1.022 for owners and 1.055 for renters, for a difference of 3.3 percentage points. For 1990, the correction ratios are 1.002 for owners and 1.045 for renters, for a difference of



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