indicators do not answer the question of whether the final match status codes were correct.
In summer 2001, Census Bureau analysts completed a Matching Error Study to evaluate the quality of the A.C.E. matching criteria and procedures (Bean, 2001). The Matching Error Study involved an independent rematch in December 2000 by highly trained matching staff (technicians and analysts) of all of the P-sample and E-sample cases in one-fifth of the A.C.E. block clusters (2,259 clusters). The Matching Error Study used the original A.C.E. data on household composition and residence and not any data from evaluation studies, so that it could measure the extent of matching error only, not confounded with measurement error. The study assumed that agreement of the original (production) and rematch codes, or agreement of an analyst in conflicting cases with either the production or the rematch code would produce match codes as close to truth as was possible. The study also assumed that the production matching and the evaluation rematching were independent—Matching Error Study rematchers did not review clusters that they worked on during the original A.C.E. and did not have access to the original match codes. Bean (2001:3) notes some minor ways in which independence could have been compromised.
A comparison of the results of the Matching Error Studies for the A.C.E. (Bean, 2001) and the PES (Davis and Biemer, 1991a,b) provides evidence of improved matching quality in the A.C.E. over the PES. For the four final P-sample match codes (match, nonmatch, remove from the P-sample, and unresolved), the A.C.E. matching error study estimated only a 0.4–0.5 percent gross difference rate compared with a 1.5 percent gross difference rate for the PES.8 The net difference rate was also reduced in the A.C.E. from the PES (0.4 and 0.9 percent, respectively).9 Gross and net difference rates for classification of E-sample cases (correct enumeration, erroneous enumeration, unresolved) were also substantially reduced in the A.C.E. from the PES (0.5–0.6 percent and 2.3 percent gross difference rates, respectively; 0.2 and 1.1 percent net difference rates, respec-