tiunit structures that lacked individual apartment addresses. For example, an apartment designated as unit “A” on the MAF by the Census Bureau may have picked up and completed the questionnaire for unit “B,” while the “B” household failed to respond. In follow-up the Census Bureau would return to apartment “A” and obtain a second interview. Reinstating the second questionnaire for “A” would effectively result in a whole-household imputation for “B” (see Hogan, 2000b).

Duplicates and other erroneous housing unit addresses in the MAF that were not involved in the special unduplication operation were probably present in the MAF, and the MAF probably omitted some valid addresses as well. A housing unit coverage study, which developed dual-systems estimates for housing units from the A.C.E. data (Barrett et al., 2001:Table 2), estimated that 1.5 percent of occupied housing units in the A.C.E. E-sample of census enumerations (excluding reinstated records) were erroneously enumerated (about 1.6 million units, weighted up to national totals) and that 2.6 percent of occupied housing units in the independent A.C.E. P-sample were omitted from the MAF (about 2.7 million units, weighted). The dual-systems estimate of occupied units, when compared with the census count (including reinstated records), produced an estimated net undercount of 0.3 percent, or about 0.4 million net occupied units omitted from the census.16

By type of structure, the housing unit coverage study estimated that small multiunit structures (those with two to nine housing units) had greater percentages of erroneous enumerations and omissions than either single-family units or large multiunit structures (Barrett et al., 2001:Table 6; see also Jones, 2003a; Ruhnke, 2003). This finding accords with evidence from the special unduplication study and the experience of LUCA participants.


The estimated net undercount of occupied housing units has not been fully reconciled with the estimated net overcount of people. See Robinson and Wolfgang (2002:i–ii), who find broad agreement among coverage patterns for regions and housing tenure between Revision II A.C.E. and the housing unit coverage study, but differences for some race/ethnicity groups. Revision II A.C.E. also estimates greater reductions in differential coverage errors between 1990 and 2000 than does the housing unit coverage study (which was based on the original A.C.E. and never reestimated).

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