To carry out the 2000 Census’s  Accuracy and Coverage Evaluation program (A.C.E. While the A.C.E. In the end, the Bureau decided not to use A.C.E.’s matching process results  to adjust the 2000 Census. To identify the extent of the census errors not accounted for by A.C.E., we  reviewed the descriptive coverage error estimates and the limitations and  context of these data as described in the Bureau reports published by the  Bureau in March 2001, October 2001, and March 2003. However, the Bureau has not accounted for how these  design decisions have affected coverage error estimates, which has  prevented it from pinpointing what went wrong with A.C.E., and this in turn  could hamper its efforts to craft a more successful coverage measurement  program for the next national head count. According to senior Bureau officials, increasingly complicated  social factors, such as extended families and population mobility,  presented challenges for A.C.E., making it difficult to determine exactly  where certain individuals should have been counted. These revisions  suggest that the original A.C.E. estimates were unreliable. estimates. Unexpected Differences in Patterns of Coverage Error between the Housing and the Population Count Further Call into Question Reliability of Revised Estimates

According to Bureau reporting, when it examined the validity of the revised  coverage error estimates the Bureau expected to see across demographic  groups similar patterns between the coverage error for the count of the  population and the count of housing. estimates has provided lessons, it remains unclear how the Bureau will use  its published coverage error estimates to make decisions leading to a more  reliable measure of coverage error in 2010, or how the unreliable estimates  can be of value to policymakers or the public. Recommendations for Executive Action

As the Bureau plans for its coverage evaluation of the next national head  count in 2010, we recommend that the Secretary of Commerce direct that  the Bureau take the following three actions to ensure that coverage  evaluation results the Bureau disseminates are as useful as possible to  Congress and other census stakeholders:  To avoid creating any unnecessary blind spots in the 2010 coverage  evaluation, as the Bureau plans for its coverage evaluation in 2010, it  should take into account how any significant future design decisions  relating to census (for example, residence rules, efforts to detect and  reduce duplicates, or other procedures) or A.C.E. might have affected the accuracy of the coverage error  estimates. 2. Regarding our finding that the Bureau has not produced reliable revised  estimates of coverage error for the 2000 Census, and, specifically, that  the full impact of the Bureau’s methodological limitations on the  revised estimates has not been made clear, the Department wrote that  the Census Bureau feels that further evaluations would not be a wise  use of resources. Residence Rules

The rules the Bureau uses to determine where people should be counted.
Why GAO Did This Study

Evaluations of past censuses show that certain groups were undercounted compared to other groups, a problem known as "coverage error." To address this, the Census Bureau included in its 2000 Census design the Accuracy and Coverage Evaluation Program (A.C.E.) to (1) measure coverage error and (2) use the results to adjust the census, if warranted. However, the Bureau found the A.C.E. results inaccurate and decided not to adjust or plan for adjustment in 2010. Congress asked GAO to determine (1) factors contributing to A.C.E.'s reported failure to accurately estimate census coverage error, and (2) the reliability of the revised coverage error estimates the Bureau subsequently produced. To do this, GAO examined three sets of Bureau research published in March 2001, October 2001, and March 2003 and interviewed Bureau officials.

What GAO Found

According to senior Bureau officials, increasingly complicated social factors, such as extended families and population mobility, presented challenges for A.C.E., making it difficult to determine exactly where certain individuals should have been counted thus contributing to the inaccuracy of the coverage error estimates. For example, parents in custody disputes both may have an incentive to claim their child as a resident, but the Bureau used rules for determining where people should be countedresidence rules--that did not account for many of these kinds of circumstances. Other design decisions concerning both A.C.E. and the census also may have created "blind spots" that contributed to the inaccuracy of the estimates. The Bureau has not accounted for the effects of these or other key design decisions on the coverage error estimates, which could hamper the Bureau's efforts to craft a program that better measures coverage error for the next national census. Despite having twice revised A.C.E.'s original coverage error estimates, the Bureau has no reliable estimates of the extent of coverage error for the 2000 census. While both revisions suggested that the original estimates were inaccurate, in the course of thoroughly reviewing the revisions, the Bureau documented (1) extensive limitations in the revision methodology and (2) an unexpected pattern between the revised estimates and other A.C.E. data, both of which indicated that the revised coverage error estimates may be questionable themselves. Furthermore, when the Bureau published the revised estimates, it did not clearly quantify the impact of these limitations for readers, thus preventing readers from accurately judging the overall reliability of the estimates. It is therefore unclear how A.C.E. information will be useful to the public or policymakers, or how the Bureau can use it to make better decisions in the future.