supporting statement B

3

B. Description of Statistical Methodology

1. Universe and Respondent Selection

The sample universe for the ITS is all persons 16 years of age and older in NCVS interviewed households.

We expect approximately 82,000 eligible persons 16 years of age and older in NCVS sample households will be eligible for the ITS from January through June 2008.

In the national sample interviewers are able to obtain interviews with 85-86 percent of household members in 90-91 percent of the occupied units in sample in any given month. Furthermore, for recent supplements to the NCVS, there is usually another 10 percent person nonresponse for the supplement.

2. Procedures for Collecting Information

In the national sample there are approximately 60,100 designated households, in clusters of four, in 694 primary sampling units located throughout the U.S. The sample consists of six parts, each of which is designated for interview in a given month and again at six-month intervals; for example, July and January, August and February, September and March, and so forth. In January 2008 the 1990 design sample will have been completely phased-out and replaced by households selected from the 2000 sample design.

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 fills or updates an automated NCVS control card within the BLAISE CAPI instrument for the household and fills the personal characteristics and crime screen question for each member 12 years old or older. The interviewer then fills a crime incident report for each reported crime incident. Each household member provides the information by self-response. The NCVS interview is always collected for each eligible respondent before the first supplement question is asked.

The first contact with a household is by personal visit. For the second through seventh visits, we use a combination of personal visits and telephone interviews.

3. Methods to Maximize Response

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. Household response rates are monitored on a daily basis within the automated survey control system. Person level response is measured weekly based on the receipt of weekly output data files. Household and person level response rates are compared to the previous months average to ensure their reasonableness. Regional office staff and field representatives are notified to take appropriate corrective action anytime household or person level nonresponse show a troubling trend.

4. Test of Procedures or Methods

The ITS questionnaire has undergone cognitive testing by Census Bureau staff. The usability of the automated CAPI instrument will be tested by interviewers during a full day User Test in October 2007. Further internal testing of the CAPI instrument will be conducted by Census Bureau staff including instrument developers and the project management staff. Interviewers will be provided with an ITS self-study which is mandatory to complete prior to initiating any interviews. Interviewer training is usually conducted a month prior to the first month of interview. This allows the interviewers time to familiarize themselves with the survey content and any special instrument functionality that is specific to conducting interviews for the ITS.

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 ITS supplement.