for different types of group quarters. This effort should include consideration of clearer definitions for group quarters, redesign of questionnaires and data content as appropriate, and improvement of the address listing, enumeration, and coverage evaluation processes for group quarters (Recommendation 4.4).

Much valuable information is available from the 2000 Accuracy and Coverage Evaluation (A.C.E.) Survey about the completeness of the census enumeration for the household population. Changes in estimation methods between the most recent A.C.E. Revision II, completed in March 2003, and the 1990 Post-Enumeration Survey (PES) make it difficult to compare coverage estimates between the two censuses. Nonetheless, there is sufficient evidence to conclude that net undercount rates for population groups were reduced in 2000 from 1990 and, even more important, that differences in net undercount rates between historically less-well-counted groups (minorities, children, renters) and other groups were reduced as well. From this result and from analysis of available information for states and large counties and places, it is reasonable to infer that differences in net undercount rates among geographic areas were also probably smaller in 2000 compared with 1990.

The reduction in differential net undercount was an achievement of the 2000 census. Contributing to this outcome, however, were large numbers of duplicate census enumerations and large numbers of wholly imputed census records (three times as many such records as in 1990, including imputations for members of enumerated households who lacked all basic characteristics as well as imputations of people into housing units that were presumed to be occupied). Both the duplicate enumerations and the imputed records generally accounted for larger proportions of historically less-well-counted groups than of other groups.

Despite the reduced differences in net undercount rates and an estimate that the 2000 census overcounted the total population by a small percentage (a first in census history), such groups as black men and renters continued be undercounted in 2000, whereas other groups were overcounted. Reducing such differences will be an important goal for the 2010 census. Also in 2000, gross errors of er-