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 E.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 be applied to the weighted number of inmovers. The assumption was that fewer inmovers would be missed in the interviewing than outmovers, so that the number of inmovers would be a better estimate of the number of movers. PES-C differed from the procedure used in the 1990 PES (see Section 5-D.1).
It was important to conduct the P-sample interviewing as soon as possible after Census Day, so as to minimize errors by respondents in reporting the composition of the household on April 1 and to be able to complete the interviewing in a timely manner. However, independence of the P-sample and E-sample could be compromised if A.C.E. interviewers were in the field at the same time as census nonresponse follow-up interviewers. An innovative solution for 2000 was to conduct the first wave of interviewing by telephone, using a computerized questionnaire. Units that were eligible for