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The Bureau of Justice Statistics also sponsors and analyzes the National Crime Victimization Survey (NCVS) and ongoing national household survey that was begun in 1972 to collect data on personal and household victimization experiences. All persons 12 years of age and older are interviewed in approximately 50.000 households every six months throughout the Nation. There are approximately 650 variables on the NCVS data file. ranging from the type of crime committed, the time and place of occurrence. and whether or not the crime was reported to law enforcement authorities. The average size of the data file for all crimes reported for a particular calendar year is 120 megabytes.

The NCVS utilizes a hierarchical file structure for its data records. In the NCVS there are four types of records: a household link record, followed by the household, personal. and incident records. The household record contains information about the household as reported by the respondent and characteristics of the surrounding area as computed by the Bureau of the Census. The person record contains information about each household member 12 years of age and older as reported by that person or proxy. with one record for each qualifying individual. Finally, the incident record contains information drawn from the incident report, completed for each household or person incident mentioned during the interview. The NCVS is a somewhat smaller data set than NIBRS. but may be considered analytically more complex because 1) there is more information available for each incident and 2) it is a panel design, i.e., the persons in each housing unit are interviewed every six months for a period of three years, thereby allowing for some degree of limited longitudinal comparison of households over time.

4 Data Utilization

An example of how those interested in the study of crime can tap the potentially rich source of new information represented by NIBRS is seen in the current Supplementary Homicide Reports data published annually by the FBI in its Crime in

the United States series. Crosstabulations of various incident-based data elements are presented, including the age, sex, and race of victims and offenders, the types of weapon(s) used, the relationship of the victim to the offender, and the circumstances surrounding the incident (for example, whether the murder resulted from a robbery, rape, or argument). The NIBRS data will offer a variable set similar in scope.

Currently, portions of eight states are reporting NIBRS data to the FBI. In 1991. three small states reported 500,000 crime incidents that required approximately one gigabyte of storage. If current NIBRS storage demands were extrapolated to full nationwide participation. 40 gigabytes of storage would be needed each year.

Although full nationwide participation in NIBRS is not a realistic short-term expectation. it is realistic to expect that a fourth of the U.S. could be represented in NIBRS within the next several years. The corresponding volume of data, 10 gigabytes each year. could still be problematic for storage and analysis.

Certain strategies may be chosen to reduce the size of the corresponding NIBRS data files. For example, most users of NIBRS data may not need or desire a data file that contains

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