What Is NIBRS?
MULTI-LEVEL DATA FILE
The NIBRS data file for Group "A" Incident Reports is structured in levels. Effective manipulation of the file requires an understanding of the levels and how they branch so that the linkages can be followed and the appropriate unit of analysis selected for research questions. (See Annotated Bibliography for Yoshio Akiyama's 1998 report for a detailed explanation.)
Each originating locale submits multiple Group "A" Offense Incident Reports. Each report consists of multiple data segments. Most data segments can consist of multiple records, each of which comprises several data elements. Most of the data elements are single valued, but some can have multiple valid values. Some of the data elements are required, but others are not.
For additional information on these topics, see the following sections:
MULTIPLE DATA SEGMENTS PER INCIDENT REPORT
A segment in NIBRS is a set of related data elements that describe an aspect of a reported crime incident.
A complete Group "A" Offense Incident Report comprises six data segments: administrative, offense, property, victim, offender, and arrestee. Each Group "A" Offense Incident Report must include the administrative, offense, victim, and offender data segments at the time of submission. The submission of the property segment and the arrestee segment are conditioned upon the type of offense and the occasion of an arrest, respectively.
A Group "B" Offense Arrest Report consists only of one data segment, which is the arrestee segment; the other incident-level data are not collected for this group of offenses.
MULTIPLE RECORDS PER DATA SEGMENT
A single Group "A" Offense Incident Report, which comprises at least four and no more than six data segments, can have multiple records in all of the segments except the administrative data segment.
The offense data segment can contain up to 10 types of offenses, each of which will trigger a separate offense segment record. The FBI's Uniform Crime Reporting hierarchy rule for selecting only the most serious offense in an incident for summary reporting is not used in NIBRS. Therefore, in multiple crime incidents all offenses (up to a maximum of the 10 most serious) are reported. Each type of offense is recorded once per incident regardless of the number of counts or perpetrators.
The victim data segment in a Group "A" Offense Incident Report can contain up to 999 records wherein each record contains detailed information pertinent to each victim. Similarly, the offender segment can contain up to 99 unique offender records and the arrestee segment can have up to 99 unique arrestee records. The property segment can contain up to 6 types of property loss, each of which corresponds to a separate property segment record that can be further described by 10 different types of property and other details.
The Group "B" Offense Arrest Report, which comprises only one data segment, can contain up to 99 separate arrestee segment records.
LINKS BETWEEN DATA SEGMENTS
In a single Group "A" Offense Incident Report, the originating agency number (ORI) and the incident number link each data segment and its records to the other data segments and records of that incident report. Each record in each data segment contains the ORI number and the incident number so that the records can be linked at both the segment level and the incident report level.
In the victim segment, there is a direct link between the victim and the offense(s) in each victim record. Each victim is assigned a unique sequential number and each offense committed against that victim is identified by the offense code. There is also a direct link between the victim and the offender(s) in the victim segment. In a victim record, the offender sequence numbers are listed for each offender who offended that victim. For each victim/offender pairing, the relationship of the victim to the offender is also captured in the victim segment.
There are also some assumed links between data segments. For example, all offenders are considered responsible for all offenses in the incident. All offenses in an incident are assumed to have been committed at the same date, time, and location. An arrest clears an incident; there is not a one-to-one relationship between arrests and offenses.
CHARACTERISTICS OF DATA ELEMENTS
Data elements have many characteristics (e.g., definitions, field types, missing values) that define them and how they can be used to answer questions. There are two particular features of the data elements in the NIBRS file that must be considered in data preparation, analysis, and interpretation: