tively). A measure of proportionate error for matches and correct enumerations for 16 aggregated poststratum groups showed smaller errors and less variation in the degree of error among groups in the A.C.E. than in the PES (Bean, 2001:Tables 5b, 5c).

Despite the improved quality of matching in the A.C.E. compared with the PES, matching error still affected the original DSE population estimates for 2000. It significantly decreased the original P-sample match rates for the nation as a whole and for 2 of 16 aggregated poststratum groups (minority and nonminority renters in large or medium metropolitan mailback areas with high return rates). It did not, however (assuming correct information on residence), significantly affect the original E-sample correct enumeration rates for the nation or any of the 16 groups. The effect of matching error on the ratio of the match rate to the correct enumeration rate resulted in an overstatement of the 2000 DSE total population estimate by about 0.5 million people (Bean, 2001:20), which amounts to an overstatement of the net undercount of about 0.2 percentage points.

The TES operation in the A.C.E. was designed to reduce the variance and bias in match and correct enumeration rates that could result from geocoding errors (i.e., assignment of addresses to the wrong block) in the census or in the P-sample address listing. In a sample of block clusters for which there was reason to expect geocoding errors (2,177 of 6,414 such clusters), the clerical search for matches of P-sample and census enumerations and for correct E-sample enumerations was extended to one ring of blocks surrounding the A.C.E. block cluster. Sampling was designed to make the search more efficient than in 1990, as was targeting the search in some instances to particular blocks (see Appendix E.3.b).

For the P-sample, only people in households that did not match an E-sample address (4.7 percent of total P-sample cases that went through matching) were searched in the sampled block clusters. On the E-sample side, only people in households identified as geocoding errors (3 percent of total E-sample cases) were searched in the sampled block clusters. Weights were assigned to the TES persons in the sampled block clusters to adjust for the sampling. Correspond-