The BJS National Crime Victimization Survey (NCVS) is the nation's primary source of information on criminal victimization. Each year, data are obtained from a nationally representative sample of about 240,000 persons in about 150,000 households. Persons are interviewed on the frequency, characteristics, and consequences of criminal victimization in the United States. The NCVS collects information on nonfatal personal crimes (i.e., rape or sexual assault, robbery, aggravated and simple assault, and personal larceny) and household property crimes (i.e., burglary/trespassing, motor vehicle theft, and other types of theft) both reported and not reported to the police. Survey respondents provide information about themselves (e.g., age, sex, race and Hispanic origin, marital status, education level, and income) and whether they experienced a victimization. For each victimization incident, the NCVS collects information about the offender (e.g., age, race and Hispanic origin, sex, and victim-offender relationship), characteristics of the crime (e.g., time and place of occurrence, use of weapons, nature of the injury, and economic consequences), whether the crime was reported to police, reasons the crime was or was not reported, and victim experiences with the criminal justice system.
The Bureau of Justice Statistics’ National Crime Victimization Survey (NCVS) is an annual data collection carried out by the U.S. Census Bureau. The NCVS is a self-reported survey that is administered annually from January 1 to December 31. Annual NCVS estimates are based on the number and characteristics of crimes respondents experienced during the prior 6 months, not including the month in which they were interviewed. Therefore, the 2020 survey covers crimes experienced from July 1, 2019 to November 30, 2020, and March 15, 2020 is the middle of the reference period. Crimes are classified by the year of the survey and not by the year of the crime.
Survey respondents provide information about themselves (e.g., age, sex, race and Hispanic origin, marital status, education level, and income) and whether they experienced a victimization. The NCVS collects information for each victimization incident about the offender (e.g., age, race and Hispanic origin, sex, and victim-offender relationship), characteristics of the crime (e.g., time and place of occurrence, use of weapons, nature of injury, and economic consequences), whether the crime was reported to police, reasons the crime was or was not reported, and victim experiences with the criminal justice system.
The NCVS is administered to persons age 12 or older from a nationally representative sample of households in the United States. The NCVS defines a household as a group of persons who all reside at a sampled address. Persons are considered household members when the sampled address is their usual place of residence at the time of the interview and when they have no usual place of residence elsewhere. Once selected, households remain in the sample for 3½ years, and eligible persons in these households are interviewed every 6 months, either in person or over the phone, for a total of seven interviews.
First interviews are typically conducted in person with subsequent interviews conducted either in person or by phone. New households rotate into the sample on an ongoing basis to replace outgoing households that have been in the sample for the 3½-year period. The sample includes persons living in group quarters (e.g., dormitories, rooming houses, and religious group dwellings) and excludes persons living on military bases and in institutional settings (e.g., correctional or hospital facilities) and persons who are homeless.
The 2020 NCVS data file includes 138,327 household interviews. Overall, 67% of eligible households completed an interview. Within participating households, there were 223,079 personal interviews in 2020, representing an 82% response rate among eligible persons from responding households. Victimizations that occurred outside of the United States were excluded from this report. In 2020, about 0.4% of the unweighted victimizations occurred outside of the United States.
Estimates in NCVS reports generally use data from the 1993 to 2020 NCVS data files, weighted to produce annual estimates of victimization for persons age 12 or older living in U.S. households. Because the NCVS relies on a sample rather than a census of the entire U.S. population, weights are designed to adjust to known population totals and to compensate for survey non-response and other aspects of the sample design.
NCVS data files include person, household, victimization, and incident weights. Person weights provide an estimate of the population represented by each person in the sample. Household weights provide an estimate of the U.S. household population represented by each household in the sample. After proper adjustment, both household and person weights are also typically used to form the denominator in calculations of crime rates. For personal crimes, the incident weight is derived by dividing the person weight of a victim by the total number of persons victimized during an incident as reported by the respondent. For property crimes, the incident weight and the household weight are the same because the victim of a property crime is considered to be the household as a whole. The incident weight is most frequently used to calculate estimates of the number of crimes committed against a particular class of victim.
Victimization weights used in these analyses account for the number of persons victimized during an incident and for high-frequency repeat victimizations (i.e., series victimizations). Series victimizations are similar in type but occur with such frequency that a victim is unable to recall each individual event or describe each event in detail. Survey procedures allow NCVS interviewers to identify and classify these similar victimizations as series victimizations and to collect detailed information on only the most recent incident in the series.
The weighting counts series victimizations as the actual number of victimizations reported by the victim, up to a maximum of 10. Doing so produces more reliable estimates of crime levels than only counting such victimizations once, while the cap at 10 minimizes the effect of extreme outliers on rates. According to the 2020 data, series victimizations accounted for 1.1% of all victimizations and 2.7% of all violent victimizations. Additional information on the enumeration of series victimizations is detailed in the report Methods for Counting High-Frequency Repeat Victimizations in the National Crime Victimization Survey (NCJ 237308, April 2012).
When national estimates are derived from a sample, as with the NCVS, caution must be used when comparing one estimate to another or when comparing estimates over time. Although one estimate may be larger than another, estimates based on a sample have some degree of sampling error. The sampling error of an estimate depends on several factors, including the amount of variation in the responses and the size of the sample. When the sampling error around an estimate is taken into account, estimates that appear different may not be statistically different.
One measure of the sampling error associated with an estimate is the standard error. The standard error may vary from one estimate to the next. Generally, an estimate with a small standard error provides a more reliable approximation of the true value than an estimate with a large standard error. Estimates with relatively larger standard errors are associated with less precision and reliability and should be interpreted with caution.
To generate standard errors around victimization, incidence and prevalence estimates from the NCVS, two methods can be used: (1) generalized variance function (GVF) parameters produced by the U.S. Census Bureau for BJS and (2) direct variance estimation methods. To conduct direct variance estimation, BJS uses a specialized version of Balanced Repeated Replication (BRR) estimation using Fay’s method. BRR estimation is a type of direct-replication-variance estimation. Under replicate-variance-estimation, a set of replicate weights (e.g., the NCVS typically has a set consisting of 160 replicate weights) is used to capture the sampling variance. Fay’s method is utilized for surveys that have rare outcomes in which the entire sample is necessary to properly estimate the variance. The U.S. Census Bureau produces GVF parameters for BJS, which account for aspects of the NCVS’s complex sample design and represent the curve fitted to a selection of individual standard errors, using a specialized version of BRR based on Fay’s method. GVFs express the variance as a function of the expected value of the survey estimate.
BJS conducts statistical tests to determine whether differences in estimated numbers, percentages, and rates in these reports were statistically significant once sampling error was taken into account. The primary test procedure BJS uses is the Student's t-statistic, which tests the difference between two sample estimates. Unless otherwise noted, the findings described in these reports as higher, lower, or different passed a test at the 0.05 level of statistical significance (95% confidence level) or at the 0.10 level of significance (90% confidence level). Readers should reference figures and tables in BJS reports for testing on specific findings. Caution is required when comparing estimates not explicitly discussed in BJS reports.
The estimates and standard errors of the estimates in BJS reports using NCVS data can be used to generate a confidence interval around the estimate as a measure of the margin of error. The following example illustrates how standard errors may be used to generate confidence intervals:
Based on the 2020 NCVS, the rate of violent victimization in 2020 was 16.4 victimizations per 1,000 persons age 12 or older. Using the BRR method of direct variance estimation, BJS determined that the estimated victimization rate has a standard error of 0.79. A confidence interval around the estimate is generated by multiplying the standard error by ± 1.96 (the t-score of a normal, two-tailed distribution that excludes 2.5% at either end of the distribution). Therefore, the 95% confidence interval around the 16.4 estimate from 2020 is 16.4 ± (0.79 × 1.96) or (14.84 to 17.94). In other words, if BJS used the same sampling method to select different samples and computed an interval estimate for each sample, it would expect the true population parameter (rate of violent victimization) to fall within the interval estimates 95% of the time.
Methodological changes implemented in 2006, including the decennial sample redesign that also occurred in 2016, may have affected the crime estimates for that year to such an extent that they are not comparable to estimates from other years. See Criminal Victimization, 2007 (NCJ 224390, December 2008) for more information on changes to the 2006 NCVS. Evaluation of 2007 through 2015 data from the NCVS conducted by BJS and the U.S. Census Bureau found a high degree of confidence that estimates for 2007 through 2015 are consistent with and comparable to estimates for 2005 and previous years.
To permit cross-year comparisons that were inhibited by the 2016 sample redesign, BJS created a revised data file. Estimates for 2016 are based on the revised file and replace previously published estimates. For more information, see Criminal Victimization, 2016: Revised (NCJ 252121, October 2018).