3. CAPI of a subsample of mail/CATI nonrespondents. CAPI interviewers, who operate from the Census Bureau’s 12 regional offices, may first attempt to complete an interview by telephone, but approximately 80 percent of CAPI cases require a personal visit to the sample address.

The 2000 long-form sample, in contrast, used two modes of data collection—mailout-mailback (assisted by an advance letter and reminder postcard) and personal paper-and-pencil interviewing.

There is evidence from comparisons of the 2000 long-form sample with the Census 2000 Supplementary Survey (C2SS), which used ACS procedures, that the professional, fully trained ACS CATI and CAPI interviewers, assisted by the built-in computer edits and questionnaire routing of the CATI and CAPI instruments, obtained more complete data than the minimally trained, temporary census enumerators (see Section 2-B.2). The CATI and CAPI interviews were even more complete for most items than the ACS mailout-mailback responses (National Research Council, 2004b: Table 7.5).

Yet the panel has two related concerns with the three different data collection modes in the ACS. One concern is that mode effects may bias responses for the same item in different ways. A second concern is that mode effects may vary among population groups and geographic areas because of differences in their response patterns by mode.

Survey literature documents that responses for the same item obtained in different ways—writing on a paper questionnaire, typing on an Internet questionnaire, responding over the telephone, responding in person—often have different properties (see, for example, de Leeuw, 2005; Dillman, 2000: Ch. 6). Some of these differences may be due to respondent-interviewer effects that are not present for mail or Internet reports; other differences may be due to different presentations of the items in the various modes—for example, providing marital status categories on a mail questionnaire but asking an open-ended “What is your marital status?” question in a telephone interview.

Only limited research has been conducted to date of mode effects in the ACS. Some mode differences were found in the Census Bureau studies that compared the C2SS and the 2000 long-form-sample responses for various questionnaire items, such as disability and race and ethnicity (see Section 2-B.2; see also Stern and Brault, 2005, which reports on the response effects of changing the placement of disability questions on the 2003 ACS mail questionnaire).