The TES evaluation study did find about 246,000 P-sample nonmatches and about 195,000 E-sample correct enumerations located beyond the surrounding blocks for a search. These cases should have been treated as nonresidents and geocoding errors, respectively; their inclusion as nonmatched residents and correct enumerations resulted in a slight overestimate in the DSE population estimate.

6–A.10 Poststratification

Poststratification is an important aspect of dual-systems estimation. Because research suggests that the probabilities of being included in the census or in the P-sample vary by individual characteristics, it is important to classify P-sample and E-sample cases into groups or strata for which coverage probabilities are as similar as possible within the group and as different as possible from other groups. The DSE then is performed stratum by stratum.

Counterbalancing the need for finely defined poststrata are two considerations: each poststratum must have sufficient sample size for reliable estimates, and the characteristics used to define the poststrata should be consistently measured between the P-sample and the E-sample. As an example, a census respondent whose household was in the E-sample may have reported age 30 for a household member when a different respondent for the same household in the P-sample reported the person to be age 29. The matched person, then, would contribute to the P-sample match rate for the 18- to 29-year-old poststrata and to the E-sample correct enumeration rate for the 30- to 49-year-old poststrata. Misclassification can be consequential if the proportions misclassified are large and if the coverage probabilities vary greatly for the affected poststrata. Finally, a consideration for the Census Bureau for 2000 was the need to define the poststrata in advance and to specify categories for which direct estimates could be developed without the complications of the modeling that was used in 1990.

Taking all these issues into account, the Census Bureau specified 448 poststrata in advance of the original A.C.E. (collapsed to 416 in the estimation, see Table E.3 in Appendix E). The somewhat larger number of A.C.E. poststrata, compared with the 357 poststrata used for the revised 1990 PES estimation, was made possible by the larger

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