duplications among age/sex groups were for men ages 18–29 (0.9 percent, mostly in college dormitories and prisons) and for women ages 18–29 (0.8 percent, almost entirely in college dormitories).

At least two factors contributed to the large number of duplicates in 2000. One factor—the problem-plagued development of the MAF from new and multiple sources—has already been discussed. The second factor had to do with the “usual residence” rules for the census—each U.S. resident is supposed to be enumerated once at his or her usual residence—and how these rules did or did not match people’s living situations. The rules were often not explained on the questionnaires or were unclear. In some instances, respondents did not want to follow the rules as stated. The result was often duplication of enumerations. For example, many college dormitory residents and people in prisons were counted at those locations, according to Census Bureau rules, but they were also reported by their families back home, counter to the instructions on the questionnaire. Some divorced parents with joint custody reported the children at both parents’ homes, and people with two houses (e.g., in New York and Florida) were sometimes counted in both locations. (Such double counting probably occurred mainly in follow-up operations, when enumerators at the second house were told that the owners lived there.)

From the Evaluation Follow-Up Study and the Further Study of Person Duplication, it became evident not only that the census residence rules were not always recognized in the census, but that they were not always recognized in the A.C.E., either. Consequently, the original A.C.E. substantially underestimated census duplicates. In turn, corrections for undetected duplications substantially reduced the net undercount, particularly for blacks and young people.

6–D WHAT CAN WE CONCLUDE ABOUT COVERAGE ERROR IN 2000?

Our conclusions about coverage error in the 2000 census address eight issues. They are: (6-D.1) the quality of the A.C.E. Revision II analysis and documentation; (6-D.2) comparability with the 1990 PES; (6-D.3) net coverage error at the national level and for major population groups; (6-D.4) net coverage error for subnational areas; (6-D.5) net coverage error for group quarters residents; (6-D.6) gross



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