Supporting statement B PPCS 2008.wpd

Supporting Statement

B. Description of Statistical Methodology

1. Universe and Respondent Selection

The sample universe is all persons aged 16 or older in all NCVS households. Approximately 12,386 persons a month, age 16 and older, in these households will be eligible to be interviewed for the supplement during July through December 2008.

Generally, interviewers are able to obtain interviews for the NCVS with approximately 80 percent of the PPCS eligible household members in 90 percent of the occupied units in sample in any given month.

2. Procedures for Collecting Information

In the national sample there are approximately 50,915 designated households located throughout the country. The sample consists of six parts, each of which is designated for interview in a given month and again at 6-month intervals; for example, July and January, August and February, September and March, and so forth. Phase-in of the 2000 decennial Census sample for the NCVS will begin in January 2005 and be fully implemented beginning in January 2008. Therefore, the 2008 PPCS sample will be based solely on 2000 decennial Census sample.

The NCVS uses a rotating sample. The sample consists of six groups for each month of enumeration. Each of these groups stays in sample for an initial interview and six subsequent interviews. The initial interview is essentially a bounding interview, which establishes a reference period, reduces telescoping into the reference period, and enables the interviewer to avoid recording duplicate reports on subsequent visits. During the course of a 6-month period, we interview a full sample of six rotation groups--one-sixth each month. In addition, one rotation group enters the sample for its bounding interview each month.

Each interview period, the interviewer updates an NCVS control card information (demographics) for each member 12 years old or older by interviewing the household respondent. The household respondent is usually a person who is 18 years of age or older who is knowledgeable about the household and its members. Once household composition and demographics are collected the interview proceeds by asking the household respondent about their victimization experiences 6 months prior to the date of interview. If the respondent has been victimized additional questions are asked to learn more about the nature and consequences of that victimization. This is repeated for each victimization the respondents reports until all victimizations are fully documented. Once complete, the PPCS supplement will be asked, that is, as long as the respondent is 16 years of age and older. Once the PPCS is complete, the next eligible household member 12 years of age or older is asked about their victimization experiences in the last six months followed by the PPCS, if they are eligible. This process is repeated until all eligible members in the household are interviewed or are verified noninterviews. Each household member provides the information by self-response. Proxy interviews are not acceptable for the PPCS.

The first contact with a household is by personal visit. For the second through seventh visits, we encourage interviews to be conducted by telephone to reduce costs.

3. Methods to Maximize Response

The Census Bureau staff mails an introductory letter (NCVS-572(L), NCVS-573(L)) explaining the NCVS to the household before the interviewer's visit or call. The Census Bureau trains interviewers to obtain respondent cooperation and instructs them to make repeated attempts to contact respondents and complete all interviews. The interviewer obtains demographic characteristics of noninterview persons and the race of noninterview households for use in the adjustment for nonresponse.

4. Test of Procedures or Methods

Since the majority of the survey questions were tested during the previous collections conducted in 1996, 1999, 2002, and 2005, the Census Bureau plans to conduct a small-scale test of the 2008 PPCS survey questions using cognitive testing techniques. An expert panel review of the 2005 supplement questions was already conducted by the Census Bureau. A Users test will also be conducted to obtain feedback on the PPCS CAPI instrument. During this one-day Users Test, NCVS interviewers will assemble in a centralized location and navigate through the PPCS CAPI instrument to ensure the usability of the instrument. The Users Test will contain both scripted and unscripted testing and the participating interviewers will be debriefed.

5. Consultants on Statistical Aspects and Data Collection

The Census Bureau will collect all information. Mr. Stephen Ash and Ms. Barbara Blass of the Demographic Statistical Methods Division of the Census Bureau provided consultation on the statistical aspects of the supplement. Ms. Marilyn Monahan heads the Crime Surveys Branch of the Demographic Surveys Division, which manages and coordinates the NCVS and the PPCS supplement. Mr. Jeremy Shimer managed the development of the 2008 PPCS CAPI instrument.