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Saturday, November 29, 2014

Criminal Victimization in the U.S., 2013 Stats from the Bureau of Justice Statistics (BJS), U.S. Department of Justice

Re-posted by Nicholas Stix
 

U.S. Department of Justice
Office of Justice Programs
Bureau of Justice Statistics

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This file is text only without graphics and many of the tables. A Zip archive of the tables in this report in spreadsheet format (.csv) and the full report including
tables and graphics in .pdf format are available on BJS website at:
http://www.bjs.gov/index.cfm?ty=pbdetail&iid=5111

This report is one in a series. More recent editions may be available. To view a list of all in the series go to http://bjs.gov/index.cfm?ty=pbse&sid=6
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Bulletin

Criminal Victimization, 2013

Jennifer L. Truman, Ph.D., and Lynn Langton, Ph.D., BJS Statisticians

In 2013, U.S. residents age 12 or older experienced an estimated 6.1 million violent victimizations and 16.8 million property victimizations, according to the Bureau of Justice Statistics’ (BJS) National Crime Victimization Survey (NCVS). After two consecutive years of increases, the overall violent crime rate (which includes rape or sexual assault, robbery, aggravated assault, and simple assault) declined slightly, from 26.1 victimizations per 1,000 persons in 2012 to 23.2 per 1,000 in 2013 (figure 1). The slight decline in simple assault accounted for about 80% of the change in total violence. The rate of violent crime in 2013 was similar to the rate in 2011 (22.6 per 1,000). Since 1993, the rate of violent crime has declined from 79.8 to 23.2 victimizations per 1,000 persons age 12 or older.

The overall property crime rate (which includes household burglary, theft, and motor vehicle theft) decreased from 155.8 victimizations per 1,000 households in 2012 to 131.4 victimizations per 1,000 in 2013. The decline in theft accounted for the majority of the decrease in property crime. Since 1993, the rate of property crime has declined from 351.8 to 131.4 victimizations per 1,000 households.

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HIGHLIGHTS
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Violent crime
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* The rate of violent crime declined slightly from 26.1 victimizations per 1,000 persons in 2012 to 23.2 per 1,000 in 2013. [A drop of 11.1% in one year doesn’t sound slight to me. Why hide your light under a bushel?]

* No statistically significant change was detected in the rate of serious violent crime (rape or sexual assault, robbery, and aggravated assault) from 2012 to 2013 (7.3 per 1,000).

* From 2012 to 2013, no statistically significant changes occurred in the rates of domestic violence, intimate partner violence, violence resulting in an injury, or violence involving a firearm.

* Violent crimes committed by a stranger decreased from 10.3 per 1,000 in 2012 to 7.9 per 1,000 in 2013.

* In 2013, 46% of violent victimizations and 61% of serious violent victimizations were reported to police.

Property crime
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* The rate of property crime decreased from 155.8 victimizations per 1,000 households in 2012 to 131.4 per 1,000 in 2013.

Prevalence of crime
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* In 2013, 1.2% of all persons age 12 or older (3 million persons) experienced at least one violent victimization. About 0.4% (1.1 million persons) experienced at least one serious violent victimization.

* The prevalence rate of violent victimization declined from 1.4% of all persons age 12 or older in 2012 to 1.2% in 2013.

* In 2013, 9% of all households (11.5 million households) experienced one or more property victimizations.
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No significant change occurred in the rate of serious violent crime
from 2012 to 2013
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There was no statistically significant change in the rate of serious violent crime—defined as rape or sexual assault, robbery, and aggravated assault—from 2012 (8.0 per 1,000) to 2013 (7.3 per 1,000) (table 1). In 2013, the rates of total violent crime and serious violent crime were lower than the rates observed a decade earlier in 2004.

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The National Crime Victimization Survey (NCVS)
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The NCVS collects information on nonfatal crimes reported and not reported to the police against persons age 12 or older from a nationally representative sample of U.S. households. Initial NCVS interviews are conducted in person with subsequent interviews conducted either in person or by phone. In 2013, the response rate was 84% for households and 88% for eligible persons. The NCVS produces national rates and levels of violent and property victimization, as well as information on the characteristics of crimes and victims, and the consequences of victimization. Since NCVS is based on interviews with victims, it does not measure homicide.

The NCVS measures the violent crimes of rape or sexual assault, robbery, aggravated assault, and simple assault. The NCVS classifies rape, sexual assault, robbery, and aggravated assault as serious violent crimes.
Property crimes include household burglary, motor vehicle theft, and theft. The survey also measures personal larceny, which includes pickpocketing and purse snatching. For additional estimates not included in this report, see the NCVS Victimization Analysis Tool (NVAT) on the BJS website.

Victimization is the basic unit of analysis used throughout most of this report. A victimization is a crime as it affects one person or household. For personal crimes, the number of victimizations is equal to the number of victims present during a criminal incident. The number of victimizations may be greater than the number of incidents because more than one person may be victimized during an incident. Each crime against a household is counted as having a single victim—the affected household.

The victimization rate is a measure of the occurrence of victimizations among a specified population group. For personal crimes, the victimization rate is based on the number of victimizations per 1,000 residents age 12 or older. For household crimes, the victimization rate is calculated using the number of incidents per 1,000 households. Estimates are presented for 2013, 2012, and then for 2004, the 10-year
change.
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Violence committed by a stranger decreased from 2012 to 2013
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The rate of domestic violence—crime committed by intimate partners and family members—remained flat from 2012 to 2013 (4.2 per 1,000). No measurable change was detected from 2012 to 2013 in rates of intimate partner violence (2.8 per 1,000), which includes victimizations committed by current or former spouses, boyfriends, or girlfriends.

Violent victimizations committed by a stranger decreased from 10.3 victimizations per 1,000 persons in 2012 to 7.9 per 1,000 in 2013. The rates of domestic violence, intimate partner violence, and violence committed by a stranger in 2013 were lower than rates in 2004. No statistically significant difference was found in the rates of serious violent crime involving weapons (4.4 per 1,000) or resulting in injury to the victim (2.8 per 1,000) from 2012 to 2013. The rate of serious violent crime involving weapons in 2013 was lower than the rate in 2004.

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No statistically significant change occurred in firearm violence from 2012 to 2013
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There was no statistically significant change in the rate of firearm violence from 2012 (1.8 per 1,000) to 2013 (1.3 per 1,000) (table 2). The rate of firearm violence in 2013 was slightly lower than the rate in 2004 (1.9 per 1,000). In 2013, there were 332,950 nonfatal firearm victimizations, compared to 460,720 in 2012. In 2013, about 75% of all serious violent crimes that involved a firearm were reported to police. There was no measurable change in the percentage of firearm violence
reported to police from 2012 to 2013.

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Thefts accounted for the majority of the decrease in property crime
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After increasing for 2 years, the number and rate of property crime victimization decreased from 2012 to 2013 (table 3). The rate of property crime victimization decreased from 155.8 victimizations per 1,000 households in 2012 to 131.4 per 1,000 in 2013, and was driven primarily by a decrease in theft. The rate of theft
decreased from 120.9 victimizations per 1,000 households in 2012 to 100.5 per 1,000 in 2013. The rate of household burglary decreased from 29.9 victimizations per 1,000 households in 2012 to 25.7 per 1,000 in 2013, while no measurable change occurred in the rate of motor vehicle theft during the same period (about 5 per 1,000). In 2013, the rates of property crime, burglary, theft, and motor vehicle theft were lower than the rates in 2004.

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Prevalence of crime
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Annual estimates of a population’s risk for criminal victimization can be examined using victimization rates or prevalence rates. Historically, BJS reports using NCVS data rely on victimization rates, which measure the extent to which victimizations occur in a specified population during a specific time. Victimization rates are used throughout this bulletin. For crimes affecting persons, NCVS victimization rates are estimated by dividing the number of victimizations that occur during a specified time (T) by the population at risk for those victimizations and multiplying the rate by 1,000.

Number of victimizations experienced by a specified population T
Victimization rate T = Number of persons in the specified populationT

Prevalence rates also describe the level of victimization but are based on the number of unique persons (or households) in the population who experienced at least one victimization during a specified time. The key distinction between a victimization rate and a prevalence rate is whether the numerator consists of the number of victimizations or the number of victims. For example, a person who experienced two robberies on separate occasions within the past year would be counted twice in the victimization rate but counted once in the prevalence rate. Prevalence rates are estimated by dividing the number of victims in the specified
population by the total number of persons in the population and multiplying the rate by 100. This is the percentage of the population victimized at least once in a given period.

Number of victims in a specified population T
Prevalence rate T = Number of persons in the specified population T

Victimization and prevalence rates may also be produced for household crimes, such as burglary. In these instances, the numerators and denominators are adjusted to reflect households rather than persons. To better understand the percentage of the population that is victimized at least once in a given period, prevalence rates are presented by type of crime and certain demographic characteristics. (For further information about measuring prevalence in the NCVS, see Measuring the Prevalence of Crime with the National Crime Victimization Survey (NCJ 241656, BJS web, September 2013).

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In 2013, 0.4% of all persons age 2 or older experienced serious violence
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In 2013, 1.2% of all persons age 12 or older (3 million persons) experienced at least one violent victimization (table 4). During the same period, about 0.4% of all persons age 12 or older (1.1 million persons) experienced at least one serious violent victimization (rape or sexual assault, robbery, and aggravated assault). The prevalence rate of violent victimization declined from 1.4% of all persons age 12 or older in 2012 to 1.2% in 2013. No measurable change occurred in the prevalence rate of serious violent victimization from 2012 to 2013. During the same period, prevalence rates of robbery (0.1%) and simple assault (0.8%) also declined.

Less than 1% of all persons age 12 or older experienced one or more domestic violence (0.2%) or intimate partner violence (0.1%) victimizations in 2013. No measurable change occurred in the prevalence rates of domestic violence and intimate partner violence from 2012 to 2013. The prevalence of violence committed by strangers declined from 0.6% of all persons age 12 or older in 2012 to 0.5% in 2013.

In 2013, 9.0% of all households (11.5 million households) experienced one or more property victimizations. The prevalence rate of property victimization declined from 10.4% in 2012 to 9.0% in 2013. During the same period, the prevalence of household burglary and theft also declined. Similar to the property victimization rate, the decline in the prevalence rate of theft accounted for the majority of the decline in the prevalence rate of property victimization.

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Persons ages 12 to 17 had the highest prevalence of violence (2.2%)of all age groups in 2013
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In 2013, 1.2% of all males age 12 or older (1.6 million males) and 1.1% of all females (1.5 million females) experienced one or more violent victimizations (table 5). While the prevalence rate declined for both males and females from 2012 to 2013, a slightly higher percentage of males (1.2%) than females (1.1%) were victims of one or more violent crimes in 2013.

In 2013, about 57,300 Asians experienced one or more violent crimes during the year and had the lowest prevalence rate (0.4%) of the U.S. population. The percentage of the population who experienced violence was highest among American Indians or Alaska Natives (2.8%), accounting for 38,310 crime victims, and persons of two or more races (3.6%), accounting for 114,190 crime victims. Although there were over 3 times more white victims (1.9 million) than black (430,380) and Hispanic (540,130) victims in 2013, blacks (1.3%) and Hispanics (1.3%) had higher prevalence rates than whites (1.1%). This was a shift from 2004, when Hispanics (1.2%) had a lower prevalence rate than both whites (1.5%) and
blacks (1.7%).

The prevalence of violence declined for whites, blacks, and Asians from 2012 to 2013. Among Hispanics and American Indians or Alaska Natives, there was no significant change in the percentage of the population that experienced one or more violent crimes during the year. Among persons of two or more races, the prevalence rate increased from 2.0% of the population experiencing violence in 2012 to 3.6% in 2013.

In 2013, 545,370 persons ages 12 to 17, or about 2.2% of all persons ages 12 to 17, experienced at least one violent crime. Persons ages 12 to 17 had the highest prevalence of violence of all age groups. In comparison, persons age 65 or older had the lowest prevalence rate with 0.3% of the population experiencing one or more violent crimes. From 2012 to 2013, the prevalence of violent crime declined for persons ages 18 to 24, ages 25 to 34, and age 65 or older.

Persons who were never married had a higher prevalence rate of violence (1.8%) than persons who were married (0.6%). Persons who were separated had the highest prevalence of violence, with 3.3% experiencing one or more violent crimes. From 2012 to 2013, the prevalence of violence declined among both persons who were never married and persons who were married, but the rate remained flat for persons of all other marital statuses.
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In 2013, 46% of violent victimizations were reported to police
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The NCVS allows for an examination of crimes reported and not reported to police. Victims may not report the victimization for a variety of reasons, including fear of reprisal or getting the offender in trouble, believing that police would not or could not do anything to help, and believing the crime to be a personal issue or trivial. Police notification can come from the victim, a third party (including witnesses, other victims, household members, or other officials, such as school officials or workplace managers), or police being at the scene of the incident. Police notification may occur during or immediately following a criminal incident or at a later date.

From 2012 to 2013, there was no statistically significant change in the percentage of violent and serious violent victimizations reported to police (table 6). In 2013, 46% of violent victimizations and 61% of serious violent victimizations were reported to police. A greater percentage of robbery (68%) and aggravated assault (64%) were reported to police than simple assault (38%) and rape or sexual assault (35%) victimizations.

From 2012 to 2013, the percentage of property victimizations reported to police increased from 34% to 36%. The percentage of reported thefts increased from 26% to 29% during the same period, accounting for the majority of the increase in the overall percentage of property victimizations reported to police. No measurable change was detected in the percentage of burglaries and motor vehicle thefts reported to police from 2012 to 2013. Similar to previous years, a larger percentage of motor vehicle thefts (75%) than burglaries (57%) and other thefts (29%) were reported to police in 2013.

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Rates of property crime reported and not reported to police declined from 2012 to 2013
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From 2012 to 2013, no differences were detected in the overall rates of violence reported and not reported to police (table 7). Among violent and serious violent victimizations reported to police, the only significant change from 2012 to 2013 was in the rate of violence committed by a stranger, which declined slightly from 5.1 to 3.9 victimizations per 1,000 persons age 12 or older. There was no significant change in the rates of domestic violence or intimate partner violence reported to police from 2012 to 2013. Among violent victimizations not reported to police, the rates of robbery, violence and serious violence committed by a stranger, and serious violent crime involving weapons declined from 2012 to 2013. The rates of robbery declined slightly from 1.2 victimizations per 1,000 in 2012 to 0.8 per 1,000 in 2013. The rates of unreported violence committed by a stranger declined slightly from 5.0 per 1,000 in 2012 to 3.8 per 1,000 in 2013. For other types of violence, the rates of unreported victimization were similar in 2012 and 2013.

In comparison, overall rates of property crime reported and not reported to police declined from 2012 to 2013. The overall rate of property crime reported to police decreased from 52.2 to 47.4 victimizations per 1,000 households. This decline was driven largely by a decrease in thefts reported to police from 2012 (31.9 per 1,000) to 2013 (28.7 per 1,000). The rate of unreported property crime declined from 101.9 victimizations per 1,000 households in 2012 to 83.1 per 1,000 in 2013. Among specific crime types that went unreported, the rate of unreported burglaries
declined from 13.2 per 1,000 in 2012 to 10.9 in 2013, and the rate of unreported theft decreased from 87.7 to 71.0 victimizations per 1,000 households. There was no change in the rate of reported or unreported motor vehicle theft victimizations from 2012 to 2013.

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In 2013, 10% of violent crime victims received assistance from a victim service agency
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Victim service agencies are publicly or privately funded organizations that provide victims with support and services to aid their physical and emotional recovery, offer protection from future victimizations, guide them through the criminal justice system process, and assist them in obtaining restitution. In 2013, about 10% of victims of violent crime received assistance from a victim service agency, which was not statistically different from 2012 (table 8). There was also no statistical difference in the percentage of victims who received assistance in 2004 compared to 2013. In 2013, a greater percentage of victims of serious violence (14%) received assistance than victims of simple assault (8%).

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Violent crime decreased for males but did not change significantly for females
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From 2012 to 2013, the rate of violent victimization for males declined from 29.1 victimizations per 1,000 males to 23.7 per 1,000 (table 9). Unlike in 2012 when males had a higher rate of victimization than females, there was no significant difference in male (23.7 per 1,000) and female (22.7 per 1,000) violent victimization rates in 2013.

The rate of violent victimization for blacks declined from 34.2 victimizations per 1,000 in 2012 to 25.1 per 1,000 in 2013. Both the rates for whites and Hispanics remained flat from 2012 to 2013. Unlike in 2012, the rates of violent crime for blacks (25.1 per 1,000), whites (22.2 per 1,000), and Hispanics (24.8 per 1,000) were similar in 2013 due to the decline in the rates for blacks.

From 2012 to 2013, violent victimization rates declined for persons ages 35 to 49, from 29.1 to 20.3 victimizations per 1,000. There was no measurable change in the rates of violent or serious violent crime for all other age groups. In 2013, persons ages 12 to 17 (52.1 per 1,000) had a higher rate of violent victimization than persons in other age groups.

With the exception of persons who were married, rates of violent victimization remained flat from 2012 to 2013 for persons of all marital statuses. Violent victimization rates for persons who were married decreased from 13.5 victimizations per 1,000 persons in 2012 to 10.7 per 1,000 in 2013. Persons who were married (10.7 per 1,000) had a lower rate of violence than persons who were never married (36.3 per 1,000), divorced (34.4 per 1,000), or separated (73.2 per 1,000). Persons who were separated had the highest rate of violence in 2013. The NCVS collects information on a respondent’s marital status at the time of the
interview but does not obtain marital status at the time of the incident. For example, persons who are separated may have experienced a victimization while married.

Violent victimization in urban areas declined from 2012 to 2013 From 2012 to 2013, the rate of violent victimization for persons living in the South declined slightly, from 22.1 victimizations per 1,000 persons to 18.0 per 1,000 (table 10). The rate of violence in the West declined from 35.5 victimizations per 1,000 persons to 27.3 per 1,000. The declines in these two regions largely accounted for the slight decline in the rate of overall violence, as there were no statistically
significant changes in rates of violent victimization in the Northeast or Midwest from 2012 to 2013. There was a slight increase in the rate of serious violence in the Northeast, from 4.6 victimizations per 1,000 in 2012 to 7.8 per 1,000 in 2013, but no other regions experienced a change in serious violence.

Urban areas accounted for most of the slight decline in the overall rate of violent victimization. The rate of violence declined in urban areas, from 32.4 to 25.9 victimizations per 1,000. There was no measurable change in the rates of violent victimization in suburban or rural areas from 2012 to 2013. Rates of serious violence did not show a statistically significant change in any of the three areas.

From 2012 to 2013, property crime rates decreased in all regions of the country and across urban, suburban, and rural areas. In 2013, property crime rates were highest in the West (182.1 per 1,000) and lowest in the Northeast (92.1 per 1,000). Urban areas (165.3 per 1,000) had a higher rate of property crime than suburban (115.3 per 1,000) and rural (109.4 per 1,000) areas.

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The NCVS and UCR showed similar Declines in property crime from 2012 to 2013
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In the first half of 2013, preliminary findings from the FBI’s Uniform Crime Reporting (UCR) program showed a decline in the number of violent and property crimes (table 11). The Bureau of Justice Statistics’ National Crime Victimization Survey (NCVS) also showed a significant decline in property crime victimization from 2012 to 2013 (down 15%) and a slight decline in violent victimizations (down 10%).

Because the NCVS and UCR measure an overlapping, but not identical, set of offenses and use different methodologies, congruity between the estimates is not expected. Throughout the 40-year history of the NCVS, both programs have generally demonstrated similar year-to-year increases or decreases in the levels of overall violent and property crimes. However, in recent years, this has not always been the case for certain crime types.

As measured by the UCR, violent crime includes murder and nonnegligent manslaughter, forcible rape, robbery, and aggravated assault. Property crime includes burglary, larceny-theft, and motor vehicle theft. The UCR measures crimes known to the police, occurring against both persons and businesses. The FBI obtains data on crimes from law enforcement agencies, while the NCVS collects data through interviews with victims. Additional information about the differences between the two programs can be found in The Nation’s Two Crime Measures (NCJ 246832, BJS web, September 2014).

Significant methodological and definitional differences exist between the NCVS and UCR:

* The NCVS obtains estimates of crimes both reported and not reported to the police, while the UCR collects data on crimes known to and recorded by the police.
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The UCR includes homicide, arson, and commercial crimes, while the NCVS
excludes these crime types.

* The UCR excludes simple assault and sexual assault, which are included
in the NCVS.***Fotnote *Simple assaults include attacks or attempted
attacks without a weapon resulting in either no injury or minor injury. Sexual assaults include attacks or attempted attacks generally involving unwanted sexual contact between the victim and offender that may or may not involve force***.

* The NCVS data are estimates from a nationally representative sample of U.S. households, while the UCR data are estimates based on counts of crimes reported by law enforcement jurisdictions.

* The NCVS excludes crimes against children age 11 or younger, persons in institutions (e.g., nursing homes and correctional institutions), and may exclude highly mobile populations and homeless people. However, victimizations against these persons are included in the UCR.

Given these differences, the two measures of crime should complement each other and provide a more comprehensive picture of crime in the United States.

In the first half of 2013 compared to the same period in 2012, there were consistent declines in UCR violent and property crimes known to police across all crime types. The number of NCVS property crimes reported to police also declined 8% from 2012 to 2013, while the apparent decline in the NCVS estimate of overall violent crime was not statistically significant. Among other NCVS violent crime types, the number of victimizations reported to police did not change significantly
from 2012 to 2013. However, unlike declines in the UCR’s semiannual estimates of forcible rape, robbery, and aggravated assault, the general direction of change in the NCVS estimates of rape and sexual assault, robbery, and aggravated assault appeared to be positive.
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Methodology
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Survey coverage
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The National Crime Victimization Survey (NCVS) is an annual data collection conducted by the U.S. Census Bureau for the Bureau of Justice Statistics (BJS). The NCVS is a self-report survey in which interviewed persons are asked about the number and characteristics of victimizations experienced during the prior 6 months. The NCVS collects information on nonfatal personal crimes (rape or sexual assault, robbery, aggravated and simple assault, and personal larceny) and household property crimes (burglary, motor vehicle theft, and other theft) both reported and not reported to police. In addition to providing annual level and change estimates on criminal victimization, the NCVS is the primary source of
information on the nature of criminal victimization incidents.

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 (including 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 3 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.

All first interviews are 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 3-year period. The sample includes persons living in group quarters, such as dormitories, rooming houses, and religious group dwellings, and excludes persons living in military barracks and institutional settings such as correctional or hospital facilities, and homeless persons.

Nonresponse and weighting adjustments
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In 2013, 90,630 households and 160,040 persons age 12 or older were interviewed for the NCVS. Each household was interviewed twice during the year. The response rate was 84% for households and 88% for eligible persons. Victimizations that occurred outside of the United States were excluded from this report. In 2013, less than 1% of the unweighted victimizations occurred outside of the United States and were excluded from the analyses.

Estimates in this report use data from the 1993 to 2013 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 inflate sample point estimates to known population totals and to compensate for survey nonresponse and other aspects of the sample design.

The NCVS data files include both person and household 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.

Victimization weights used in this analysis account for the number of persons present 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 weight counts series incidents as the actual number of incidents reported by the victim, up to a maximum of 10 incidents. Including series victimizations in national rates results in large increases in the level of violent victimization; however, trends in violence are generally similar, regardless of whether series victimizations are included. In 2013, series incidents accounted for about 1% of all
victimizations and 4% of all violent victimizations. Weighting series incidents as the number of incidents up to a maximum of 10 incidents produces more reliable estimates of crime levels, while the cap at 10 minimizes the effect of extreme outliers on rates. Additional information on the series enumeration is detailed in the report Methods for Counting High-Frequency Repeat Victimizations in the National Crime Victimization Survey (NCJ 237308, BJS web, April 2012).

Standard error computations
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When national estimates are derived from a sample, as with the NCVS, it is important to use caution when comparing one estimate to another estimate 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, the 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 can 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 large standard errors are associated with less precision and reliability and should be interpreted with caution.

To generate standard errors around numbers and estimates from the NCVS, the Census Bureau produced generalized variance function (GVF) parameters for BJS. The GVFs take into account aspects of the NCVS complex sample design and represent the curve fitted to a selection of individual standard errors based on the Jackknife Repeated Replication technique. The GVF parameters were used to generate standard errors for each point estimate (e.g., counts, percentages, and rates) in this report.

BJS conducted tests to determine whether differences in estimated numbers, percentages, and rates in this report were statistically significant once sampling error was taken into account. Using statistical programs developed specifically for the NCVS, all comparisons in the text were tested for significance. The primary test procedure was the Student’s t-statistic, which tests the difference between two sample estimates. Differences described as higher, lower, or different passed a test at the 0.05 level of statistical significance (95% confidence level). Differences described as somewhat, slightly, or marginally different, or with some indication of difference, passed a test at the 0.10 level of statistical significance (90% confidence level). Caution is required when comparing estimates not explicitly
discussed in this report.

Data users can use the estimates and the standard errors of the estimates provided in this report to generate a confidence interval around the estimate as a measure of the margin of error. The following example illustrates how standard errors can be used to generate confidence intervals:

*According to the NCVS, in 2013, the violent victimization rate among persons age 12 or older was 23.2 per 1,000 persons (see table 1). Using the GVFs, it was determined that the estimated victimization rate has a standard error of 1.6 (see appendix table 2). A confidence interval around the estimate was generated by multiplying the standard errors 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 23.2 estimate from 2013 is 23.2 ± (1.6 X 1.96) or (20.0 to 26.3). In others words, if different samples using the same procedures were taken from the U.S. population in 2013, 95% of the time the violent victimization rate would fall between 20.1 and 26.3 per 1,000 persons.

In this report, BJS also calculated a coefficient of variation (CV) for all estimates, representing the ratio of the standard error to the estimate. CVs provide a measure of reliability and a means to compare the precision of estimates across measures with differing levels or metrics. In cases in which the CV was greater than 50%, or the unweighted sample had 10 or fewer cases, the estimate was noted with a “!” symbol (Interpret data with caution. Estimate based on 10 or fewer sample cases, or the coefficient of variation is greater than 50%).

Methodological changes to the NCVS in 2006
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Methodological changes implemented in 2006 may have affected the crime estimates for that year to such an extent that they are not comparable to estimates from other years. Evaluation of 2007 and later data from the NCVS conducted by BJS and the Census Bureau found a high degree of confidence that estimates for 2007, 2008, 2009, 2010, 2011, 2012, and 2013 are consistent with and comparable to estimates for 2005 and previous years. The reports, Criminal Victimization, 2006, NCJ 219413, December 2007; Criminal Victimization, 2007, NCJ 224390, December 2008; Criminal Victimization, 2008, NCJ 227777, September 2009; Criminal Victimization, 2009, NCJ 231327, October 2010; Criminal Victimization,
2010, NCJ 235508, September 2011; Criminal Victimization, 2011, NCJ 239437, October 2012; and Criminal Victimization, 2012, NCJ 243389, October 2013 are available on the BJS website.

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The Bureau of Justice Statistics of the U.S. Department of Justice is the principal federal agency responsible for measuring crime, criminal victimization, criminal offenders, victims of crime, correlates of crime, and the operation of criminal and civil justice systems at the federal, state, tribal, and local levels. BJS collects, analyzes, and disseminates reliable and valid statistics on crime and justice systems
in the United States, supports improvements to state and local criminal justice information systems, and participates with national and international organizations to develop and recommend national standards for justice statistics. William J. Sabol is acting director.

This report was written by Jennifer L. Truman, Ph.D. and Lynn Langton, Ph.D. Erika Harrell verified the report.

Lockheed Martin, Jill Thomas, and Morgan Young edited the report. Barbara Quinn produced the report.

September 2014, NCJ 247648
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Office of Justice Programs
Innovation * Partnerships * Safer Neighborhoods
www.ojp.usdoj.gov
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