Dual-systems estimation in the census context requires that census enumerations be excluded from the E-sample when they have insufficient information for matching and follow-up (so-called IIs—see Section 5-A). The 2000 census had almost four times as many IIs as the 1990 census—8.2 million, or 2.9 percent of the household population, compared with 2.2 million or 0.9 percent of the population. In 2000 5.8 million people fell into the II category because they were whole-person imputations (types 1–5, as described in Section 4-D); another 2.4 million people were IIs because their records were not available in time for the matching process. These people were not in fact enumerated late; rather, they represented records that were temporarily deleted and subsequently reinstated on the census file as part of the special MAF unduplication process in summer–fall 2000 (see Section 4-E). In 1990 only 1.9 million whole-person imputations and 0.3 million late additions from coverage improvement programs fell into the II category.
Because the phenomenon of reinstated cases in the 2000 census was new and the number of such cases was large, the Bureau investigated the possible effects of their exclusion from the E-sample on the dual-systems estimate. Hogan (2001b) demonstrated conceptually that excluding the reinstated people would have little effect so long as they were a small percentage of census correct enumerations or their A.C.E. coverage rate (ratio of matches to all correct enumerations) was similar to the E-sample coverage rate. To provide empirical evidence, a clerical matching study was conducted in summer 2001 of reinstated people whose census records fell into an evaluation sample of one-fifth of the A.C.E. block clusters (Raglin, 2001). This study found that 53 percent of the reinstated records in the evaluation sample duplicated another census record (and, hence, had no effect on the DSE), 25 percent matched to the P-sample, and 22 percent were unresolved (such a large percentage resulted from the infeasibility of follow-up to obtain additional information). Using a range of correct enumeration rates for the unresolved cases, the analysis demonstrated that the exclusion of reinstated records from the E-sample had a very small effect on the DSE for the total population (less than one-tenth of 1 percent). Moreover, because