In addition to the restriction of some group quarters types from NCVS eligibility—thus excluding people like jail or prison inmates—the NCVS also restricts the coverage of the survey by age. Within units selected for the sample, NCVS interviewers are directed to obtain reports for only those individuals age 12 or older.
Furthermore, “U.S. citizens residing abroad and foreign visitors to this country” are not supposed to be included in the NCVS.
The youngest of NCVS-eligible persons—12- and 13-year-olds—are one of three cases in which proxy reporting (and not a direct interview) is permitted; if the household respondent (see Section C–3.a) insists that the interviewer not directly question a 12- or 13-year-old, questionnaire information may be taken from that household member. The other two cases in which proxy reporting is allowed are “temporarily absent household members and persons who are physically or mentally incapable of granting interviews”; in the latter instance, a person who is not a member or usual resident of the household (e.g., a professional caregiver) may provide the requested information.3
Table C-1 shows the number of sample households and the number of persons contacted in those households for the most recent years for which NCVS data are available. The table also illustrates the decline in NCVS sample size over time. When the National Crime Survey began in 1972, it reached a household sample of 72,000 households; by 2005, that sample had nearly been halved to 38,600. Some of the sample size cuts contributing to this decline are listed in Box 1-2.
The combination of a declining sample size and less crime to measure—overall, “the rate of crime remains at the lowest levels in the past thirty years” (Catalano, 2006:3)—makes it extremely difficult to discern year-to-year annual change, even in aggregate measures like the rate of all violent crime. The violent crime rates for 1993–2005 are illustrated in Figure C-1, along with boxes showing the 95 percent confidence intervals associated with those rates; significant annual change differences have been rare in the past decade. For this reason, the BJS Criminal Victimization bulletins (e.g., Catalano, 2006) make comparisons based on 2-year groups of data.