of the 2000s. The decision document (U.S. Census Bureau, 2003b:1) stated:

The Accuracy and Coverage Evaluation (A.C.E.) Revision II methodology represents a dramatic improvement from the previous March 2001 A.C.E. results. However, several technical errors remain, including uncertainty about the adjustment for correlation bias, errors from synthetic estimation, and inconsistencies between demographic analysis estimates and the A.C.E. Revision II estimates of the coverage of children. Given these technical concerns, the Census Bureau has concluded that the A.C.E. Revision II estimates should not be used to change the base for intercensal population estimates.

With the final decision not to adjust population estimates for measured net undercount in the 2000 census behind it, the Census Bureau announced its intention to focus exclusively on planning for the 2010 census. Plans for that census include work on possibly using computerized matching of the type conducted for the October 2001 and March 2003 adjustment decisions to eliminate duplicate enumerations as part of the census process itself. Bureau officials also expressed the view that coverage evaluation could not be completed and evaluated in a sufficiently timely fashion to permit adjustment of the data used for legislative redistricting (Kincannon, 2003).

In this chapter we assess the A.C.E. Revision II estimation methodology and the resulting estimates of population coverage in the 2000 census. We first review key aspects of the original A.C.E. Program (6-A) and then review the data sources, methods, and results of the A.C.E. Revision II effort (6-B). We discuss two kinds of enumerations that had more impact on coverage in 2000 than in 1990: (1) whole-person (including whole-household) imputations and (2) duplicate enumerations in the census and the A.C.E. (6-C). Section 6-D provides an overall summary of what we know and do not know about population coverage in 2000. Section 6-E provides our recommendations for coverage evaluation research and development for 2010.

6–A ORIGINAL A.C.E. DESIGN AND OPERATIONS

An important part of evaluating the Revision II A.C.E. population estimates for 2000 is to consider how well the original A.C.E.



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