TABLE 7-4 Victimizations Reported as Series Victimizations in the NCVS, by Type of Crime, 1993-1999 and 2000-2009, as Percentage of All Victimizations Reported
|Category of Victimization||1993-1999||2000-2009|
|Rape and sexual assault||6.3||5.7|
|Motor vehicle theft||0.3||0.2a|
NOTE: Table shows the number of incident reports recorded under “series victimization” procedures (which will include multiple victimizations) as a percentage of all incident reports recorded.
aInterpret with caution; estimate based on 10 or fewer sample cases, or coefficient of variation is greater than 50 percent.
SOURCE: Lauritsen et al. (2012, p. 3, Table 2).
Lauritsen et al. (2012) found some supportive evidence for this conjecture.3
From a statistical point of view, series victimization procedures create outlier problems for estimation. In general, outlier problems can be caused by large estimation weights, large outlying data values, or moderate values. Estimation weights for the NCVS are fairly large. When estimating rape and sexual assault (a low-incidence item in the NCVS data), the data values are generally zero (no rape or sexual assault reported). When rape or sexual assault is reported as a series, the data value can be quite high.4 Under the new procedures the value is truncated at “10” for individuals reporting more than 10 incidents in a single series. Even with the truncation, these outliers (representing only 6 percent of the positive responses to rape and sexual assault) tied to the NCVS weights have a substantial impact on the estimates and the standard errors of those estimates, with both increasing fairly substantially. Fortunately, the statistical literature is fairly well developed in the areas of detecting and adjusting for outliers, and some of the developed techniques (adjusting the weights, the data value, or both)
3By the definition of series victimization, the respondent must report six or more similar victimizations during the reference period for which she or he cannot recall the separate details. However, Lauritsen et al. (2012) found examples of records categorized as a series victimization in which the respondent identified fewer than six victimizations.
4Lauritsen et al. (2012, p. 10) reported a maximum value of “750” incidents in series has been reported for serious violent crimes. They did not report the maximum value reported for rape and sexual assault.