1990. These errors, which would not have been detected without the A.C.E., have greatest impact on estimates for population groups and subnational geographic areas.

Finding 1.8: The experience with the 2000 Accuracy and Coverage Evaluation Program and the evaluation of census processes and data content make clear that useful evaluation requires considerable time. In particular, it appears difficult to complete sufficiently comprehensive assessments of population coverage and the quality of basic characteristics by the currently mandated schedule for releasing block-level census data for use in redistricting (which is 12 months after Census Day).

Finding 1.9: Census counts at the block level—whether adjusted or unadjusted—are subject to high levels of error and hence should be used only when aggregated to larger geographic areas.

Finding 1.10: Under tight time constraints, the Census Bureau’s coverage evaluation technical staff conducted comprehensive and insightful research of high quality on the completeness of coverage in the 2000 census. Their results for the A.C.E. and demographic analysis were well documented and provided useful information to 2010 census planners, stakeholders, and the public.

Finding 1.11: The Census Bureau’s evaluations of census processes and the quality of the data content were slow to appear, are often of limited value to users for understanding differences in data quality among population groups and geographic areas, and are often of limited use for 2010 planning.