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 Executive Steering Committee for A.C.E. Policy (ESCAP) reviewed the initial results of the A.C.E., which were released in March 2001, and recommended that unadjusted census data be used for redistricting as analysis and evaluations indicated that there were serious errors in these estimates. After assessing considerable new evidence, the second ESCAP Committee (ESCAP II) recommended, in October 2001, that unadjusted Census 2000 data also be used for non-redistricting purposes.

Research efforts to fix the detected errors resulted in improved coverage estimates referred to as A.C.E. Revision II which was released in March 2003. 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.