at a rate of 1 in 10. However, all small block clusters that were determined to have 10 or more housing units and all small block clusters on American Indian reservations, in other American Indian areas, or in list/enumerate areas were retained. After completion of the cluster subsampling operations, the A.C.E. sample totaled about 11,000 block clusters.

The addresses on the P-sample address listing were matched with the MAF addresses in the sampled block clusters. The purpose of this match was to permit automated subsampling of housing units in large blocks for both the P-sample and the E-sample and to identify nonmatched P-sample and E-sample housing units for field follow-up to confirm their existence. Possible duplicate housing units in the P-sample or E-sample were also followed up in the field. When there were large discrepancies between the housing units on the two samples, indicative of possible geocoding errors, the block clusters were relisted for the P-sample.

After completion of housing unit matching and follow-up, the final step in developing the P-sample was to subsample segments of housing units on the P-sample address list in large block clusters in order to reduce the interviewing workload. The resulting P-sample contained about 301,000 housing units. Subsequently, segments of housing units in the census were similarly subsampled from large block clusters in order to reduce the E-sample follow-up workload. For cost reasons, the subsampling was done to maximize overlapping of the P-sample and E-sample. Table C-1 shows the distribution of the P-sample by sampling stratum, number of block clusters, number of housing units, and number of people.

The goal of the A.C.E. interviewing of P-sample households was to determine who lived at each sampled address on Census Day, April 1. This procedure required that information be obtained not only about nonmovers between Census Day and the A.C.E. interview day, but also about people who had lived at the address but were no longer living there (outmovers). In addition, the P-sample interviewing ascertained the characteristics of people who were now living at the address but had not lived there on Census Day (inmovers).

The reason for including both inmovers and outmovers was to implement a procedure called PES-C, in which the P-sample match rates for movers would be estimated from the data obtained for outmovers, but these rates would then