assigned residence probabilities to each P-sample case linked to a census enumeration outside the A.C.E. search area in the same manner as the E-sample duplicates as described in Section 6-B.1 (see also U.S. Census Bureau, 2003c:58). The reduction in nonmover residents was proportionately greater for nonmatched cases than for matched cases, which had the result of raising the P-sample match rate and lowering the DSE and net undercount overall.

The correction for measurement error for P-sample outmovers and nonmover cases that did not match to a census enumeration outside the search area was based on the results of the reanalysis of the Evaluation Follow-up Study and the Matching Error Study. The EFU reanalysis results were used to adjust residence probabilities, and the Matching Error Study results were used to correct for false matches and false nonmatches. As was the case for the E-sample, the P-sample correction factors from the EFU reanalysis and the Matching Error Study were calculated only for a small number of aggregate poststrata and not for the full set of P-sample poststrata.

On balance, the effect of the adjustments to the P-sample was to raise the match rate slightly, from 91.59 to 91.76. In turn, this increase lowered the DSE population estimate and net undercount estimates (see Section 6-B.6).

6–B.3 New Models for Missing Data

In A.C.E. Revision II, as in the original A.C.E., not all E-sample cases could be clearly assigned a status as correct or erroneous, and not all P-sample cases could be clearly assigned a status as a resident or nonresident, or, if a resident, as a match or nonmatch. Enumeration, residence, and match statuses had to be imputed to these unresolved cases. Evaluation of the original imputation procedures, which used only variables that were available after the initial matching and before follow-up to define imputation cells, indicated that they contributed significant variability, and possibly bias, to the original DSE population estimates (see Section 6-A.6). For Revision II, new imputation procedures were devised; they used variables from the evaluation follow-up data, such as whether the respondent provided an alternate Census Day address (Beaghen and Sands, 2002; Kostanich, 2003a:Ch.4). New procedures were also devised to adjust P-sample Census Day weights for households determined

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