APPENDIX IV—The Nation's Two Crime Measures

The U.S. Department of Justice administers two statistical programs to measure the magnitude, nature, and impact of crime in the Nation:  the Uniform Crime Reporting (UCR) Program and the National Crime Victimization Survey (NCVS).  Each of these programs produces valuable information about aspects of the Nation's crime problem.  Because the UCR and NCVS programs are conducted for different purposes, use different methods, and focus on somewhat different aspects of crime, the information they produce together provides a more comprehensive panorama of the Nation's crime problem than either could produce alone.

Uniform Crime Reports

The FBI's UCR Program, which began in 1929, collects information on the following crimes reported to law enforcement authorities:  homicide, forcible rape, robbery, aggravated assault, burglary, larceny-theft, motor vehicle theft, and arson.  Law enforcement agencies report arrest data for 21 additional crime categories.

The UCR data are compiled from monthly law enforcement reports or individual crime incident records transmitted directly to the FBI or to centralized state agencies that then report to the FBI.  Each report submitted to the UCR Program is examined thoroughly for reasonableness, accuracy, and deviations that may indicate errors.  Large variations in crime levels may indicate modified records procedures, incomplete reporting, or changes in a jurisdiction's boundaries.  To identify any unusual fluctuations in an agency's crime counts, monthly reports are compared with previous submissions of the agency and with those for similar agencies.

In 2002, law enforcement agencies active in the UCR Program represented approximately 288.4 million United States inhabitants—93.4  percent of the total population.

The UCR Program provides crime counts for the Nation as a whole, as well as for regions, states, counties, cities, and towns.  This permits studies among neighboring jurisdictions and among those with similar populations and other common characteristics.

UCR findings for each calendar year are published in a preliminary release in the spring of the following calendar year, then succeeded by a detailed annual report, Crime in the United States, issued in the fall.  In addition to crime counts and trends, this report includes data on crimes cleared, persons arrested (age, sex, and race), law enforcement personnel (including the number of sworn officers killed or assaulted), and the characteristics of homicides (including age, sex, and race of victims and offenders; victim-offender relationships; weapons used; and circumstances surrounding the homicides).  Other periodic reports are also available from the UCR Program.

The UCR Program is continually converting to the more comprehensive and detailed National Incident-Based Reporting System (NIBRS).  NIBRS can provide detailed information about each criminal incident in 22 broad categories of offenses.

National Crime Victimization Survey

The Bureau of Justice Statistics' NCVS, which began in 1973, provides a detailed picture of crime incidents, victims, and trends.  After a substantial period of research, the survey completed an intensive methodological redesign in 1993.  The redesign was undertaken to improve the questions used to uncover crime, update the survey methods, and broaden the scope of crimes measured.  The redesigned survey collects detailed information on the frequency and nature of the crimes of rape, sexual assault, personal robbery, aggravated and simple assault, household burglary, theft, and motor vehicle theft.  It does not measure homicide or commercial crimes (such as burglaries of stores).

Two times a year, U.S. Bureau of the Census personnel interview all household members at least 12 years old in a nationally representative sample of approximately 49,000 households (about 80,000 people).  Approximately 160,000 interviews are conducted annually. Households stay in the sample for 3 years.  New households rotate into the sample on an ongoing basis.

The NCVS collects information on crimes suffered by individuals and households, whether or not those crimes were reported to law enforcement.  It estimates the proportion of each crime type reported to law enforcement, and it summarizes the reasons that victims give for reporting or not reporting.

The survey provides information about victims (age, sex, race, ethnicity, marital status, income, and educational level), offenders (sex, race, approximate age, and victim-offender relationship), and the crimes (time and place of occurrence, use of weapons, nature of injury, and economic consequences).  Questions also cover the experiences of victims with the criminal justice system, self-protective measures used by victims, and possible substance abuse by offenders.  Supplements are added periodically to the survey to obtain detailed information on topics like school crime.

The first data from the redesigned NCVS were published in a BJS bulletin in June 1995.  BJS publication of NCVS data includes Criminal Victimization in the United States, an annual report that covers the broad range of detailed information collected by the NCVS.  BJS publishes detailed reports on topics such as crime against women, urban crime, and gun use in crime.  The NCVS data files are archived at the National Archive of Criminal Justice Data at the University of Michigan to enable researchers to perform independent analyses.

Comparing UCR and NCVS

Because the NCVS was designed to complement the UCR Program, the two programs share many similarities.  As much as their different collection methods permit, the two measure the same subset of serious crimes, defined alike.  Both programs cover rape, robbery, aggravated assault, burglary, theft, and motor vehicle theft.  Rape, robbery, theft, and motor vehicle theft are defined virtually identically by both the UCR and NCVS.  (While rape is defined analogously, the UCR Crime Index measures the crime against women only, and the NCVS measures it against both sexes.)

There are also significant differences between the two programs.  First, the two programs were created to serve different purposes.  The UCR Program's primary objective is to provide a reliable set of criminal justice statistics for law enforcement administration, operation, and management.  The NCVS was established to provide previously unavailable information about crime (including crime not reported to police), victims, and offenders.

Second, the two programs measure an overlapping but nonidentical set of crimes.  The NCVS includes crimes both reported and not reported to law enforcement.  The NCVS excludes, but the UCR includes, homicide, arson, commercial crimes, and crimes against children under age 12.  The UCR captures crimes reported to law enforcement, but it excludes simple assaults and sexual assaults other than forcible rape from the Crime Index.

Third, because of methodology, the NCVS and UCR definitions of some crimes differ.  For example, the UCR defines burglary as the unlawful entry or attempted entry of a structure to commit a felony or theft.  The NCVS, not wanting to ask victims to ascertain offender motives, defines burglary as the entry or attempted entry of a residence by a person who had no right to be there.

Fourth, for property crimes (burglary, theft, and motor vehicle theft), the two programs calculate crime rates using different bases.  The UCR rates for these crimes are per capita (number of crimes per 100,000 persons), whereas the NCVS rates for these crimes are per household (number of crimes per 1,000 households).  Because the number of households may not grow at the same rate each year as the total population, trend data for rates of property crimes measured by the two programs may not be comparable.

In addition, some differences in the data from the two programs may result from sampling variation in the NCVS and from estimating for nonresponse in the UCR.  The NCVS estimates are derived from interviewing a sample and are, therefore, subject to a margin of error.  Rigorous statistical methods are used to calculate confidence intervals around all survey estimates.  Trend data in NCVS reports are described as genuine only if there is at least a 90 percent certainty that the measured changes are not the result of sampling variation.  The UCR data are based on the actual counts of offenses reported by law enforcement jurisdictions.  In some circumstances, UCR data are estimated for nonparticipating jurisdictions or those reporting partial data.

Apparent discrepancies between statistics from the two programs can usually be accounted for by their definitional and procedural differences or resolved by comparing NCVS sampling variations (confidence intervals) of those crimes said to have been reported to police with UCR statistics.

For most types of crimes measured by both the UCR and NCVS, analysts familiar with the programs can exclude from analysis those aspects of crime not common to both.  Resulting long-term trend lines can be brought into close concordance.  The impact of such adjustments is most striking for robbery, burglary, and motor vehicle theft, whose definitions most closely coincide.

With robbery, annual victimization rates are based only on NCVS robberies reported to the police.  It is also possible to remove UCR robberies of commercial establishments such as gas stations, convenience stores, and banks from analysis.  When the resulting NCVS police-reported robbery rates are compared to UCR noncommercial robbery rates, the results reveal closely corresponding long-term trends.

Each program has unique strengths.  The UCR provides a measure of the number of crimes reported to law enforcement agencies throughout the country.  The UCR's Supplementary Homicide Reports provide the most reliable, timely data on the extent and nature of homicides in the Nation.  The NCVS is the primary source of information on the characteristics of criminal victimization and on the number and types of crimes not reported to law enforcement authorities.

By understanding the strengths and limitations of each program, it is possible to use the UCR and NCVS to achieve a greater understanding of crime trends and the nature of crime in the United States.  For example, changes in police procedures, shifting attitudes towards crime and police, and other societal changes can affect the extent to which people report and law enforcement agencies record crime.  NCVS and UCR data can be used in concert to explore why trends in reported and police-recorded crime may differ.