The U.S. Census Bureau conducted the Accuracy and Coverage Evaluation (A.C.E.) survey to measure the coverage of the population in Census 2000. The A.C.E. was designed to serve two purposes: (1) to measure the net coverage of the population, both in total and for major subgroups, and (2) to provide data that could serve as the basis for correcting the census counts for such uses as Congressional redistricting, state and local redistricting, funds allocation and governmental program administration. The A.C.E. survey provides critical information that can be used to improve the census-taking process. However, the design, methodology, operations and data collection efforts are extremely complex and not widely understood. The work described in this publication was a major undertaking, and the technical documentation is intended to increase awareness and knowledge, and subsequently improve the 2010 Census and coverage measurement techniques.

Despite the fact that coverage measurement techniques have been utilized by the Census Bureau for several decades, this is the first comprehensive documentation of its kind. This technical document describes the methodologies that were used to produce estimates of Census 2000 coverage error from the A.C.E. The first part of this document discusses the entire survey design used to produce the original estimates of net undercount released in March 2001. Analysis and evaluations indicated that there were serious errors in the March 2001 A.C.E. Research efforts to fix the detected errors resulted in improved coverage estimates referred to as A.C.E. Revision II. The second part of this document describes the methodology used to correct for errors in the March 2001 A.C.E.

After extensive analysis and consideration, the Census Bureau ultimately decided not to use the A.C.E. - neither the March 2001 nor the Revision II results - to correct the Census 2000 counts or any other data products. A.C.E. Revision II, the superior of the two results, provides useful coverage measurement information that can be used for research purposes. All of these results, decisions, supporting analyses, technical assessments, and limitations can be found on the Census Bureau’s Web site at www.census.gov/dmd/www/EscapRep.html.

This document is intended to promote knowledge and encourage collaboration on coverage measurement issues. As such, we welcome comments and suggestions from colleagues on technical issues and also on the value of this document.