cases and other cases for quality assurance. Then a yet smaller analyst staff reviewed the cases the technicians could not resolve.

Matching and correct enumeration rates would be biased if there were not a further step of follow-up in the field to check certain types of cases. On the E-sample side, almost all cases that were assigned a nonmatch or unresolved code by the computer and clerical matchers were followed up, as were people at addresses that were added to the MAF subsequent to the housing unit match. The purpose of the person follow-up was to determine if these cases were correct (nonmatching) enumerations or erroneous.

On the P-sample side, about half of the cases that were assigned a nonmatch code and most cases that were assigned an unresolved code were followed up in the field. The purpose was to determine if they were residents on Census Day and if they were a genuine nonmatch. Specifically, P-sample nonmatches were followed up when they occurred in: a partially matched household; a whole household that did not match a census address and the interview was conducted with a proxy respondent; a whole household that matched an address with no census person records and the interview was conducted with a proxy; or a whole household that did not match the people in the E-sample for that household. In addition, P-sample whole household nonmatches were followed up when: an analyst recommended follow-up; when the cluster had a high rate of P-sample person nonmatches (greater than 45 percent); when the original interviewer had changed the address for the household; and when the cluster was not included in the initial housing unit match (e.g., list/enumerate clusters, relisted clusters).

The field follow-up interviews were conducted with a paper questionnaire, and interviewers were instructed to try even harder than in the original interview to speak with a household member. After field follow-up, each P-sample and E-sample case was assigned a final match and residence status code by clerks and, in some cases, technicians or analysts.