Methods

Introduction

The data capturing detailed information on homicide incidents are collected annually by the Federal Bureau of Investigation (FBI) through its Supplementary Homicide Reporting (SHR) Program. The FBI prepares a data file containing this information and releases the file for public use. The National Center for Juvenile Justice (NCJJ) obtained incident level SHR data from the Interuniversity Consortium for Political and Social Research's (ICPSR) National Criminal Justice Data Archive (for data years 1980-2016) and from the FBI's "Crime Data Explorer" for 2017 through 2020. [See the "Data Sources" section for complete citations of the files used in this application.]

Based on analyses of these data, NCJJ modified the contents of the files by deleting incompatible data and recoding values into more general categories. NCJJ also constructed and added weights to the records so that weighted analyses would yield national estimates. A detailed explanation of the procedures used by NCJJ to create the data file that underlies this package can be found below.

While NCJJ has benefited greatly from the work of others, any errors in this analysis and data presentation package are the responsibility of the National Center for Juvenile Justice alone. This package has been made available to the public so that interested users can explore the information compiled in the FBI's Supplementary Homicide Reporting Program. However, the computation and estimation procedures incorporated into this application reflect one of many possible approaches for developing national estimates from the raw SHR data.

Data

The SHR data file received by NCJJ captured information on each homicide incident reported by law enforcement. An incident may include one or more victims and one or more offenders. In incidents where there were multiple offenders it had to be assumed that all offenders were involved in the killings of all victims. The incident information included: the name and location of the law enforcement agency reporting the incident; the year of the incident; the age, sex and race of the victim(s); the weapon(s) used; the age, sex, and race of the offender(s) when known; and the offender's relationship to each victim (when known).

From these data two separate files were created. One is a victim-based file in which each record represents one victim with associated information on the weapon used and offender(s) involved. The other file is an offender-based file where each record represents one offender with associated information on the weapon used and victim(s) involved.

To clarify the file structure, a few examples are useful. Incidents with a single victim and a single known offender would generate one record in the victim file and one record in the offender file. If the offender were unknown (i.e., no description was available at the time of reporting either because there were no witnesses, the offender was not apprehended, or the offender information was not reported to the FBI), this incident would generate one record in the victim file with missing offender information and no record in the offender file. The decision was made to create a record in the offender file only when some information was available on the offender(s) because there was no obvious technique for determining how many offenders were involved in the incident and, consequently, how many records to create.

In the few incidents with multiple victims (5%, or 981 of 18,464 incidents reported in 2020), the offender records contain information on the first victim. Versions of this application released prior to September 2010 provided information on the oldest victim. We now provide information from the first recorded victim. Data from the first victim record is more complete and more accurate in terms of the Victim-Offender relationship variable (see the section on "Handling the Victim-Offender Relationship" for more information). In incidents where there were multiple offenders, the victim records contain information on the oldest offender. Note that, in some instances, offender age is not present on the record. When this occurs, information associated with the first offender is used.

In summary the resulting victim data file contains a record on every murder victim. (All justifiable and negligent homicide incidents were deleted from the data files.) The offender file, more properly labeled the known offender file, contains a record on each offender for which some information was reported to the FBI. The SHR data are not able to track individuals across incidents; so an offender who was involved in more than one incident will have an offender record for each incident.

Victim Offender Relationship Handling

Although for incidents involving more than one victim law enforcement agencies report to the FBI information regarding the relationship of the offender(s) to each victim, the FBI only recorded offender(s) relationships with the first recorded victim in the data file.

Consider the following situation where a man kills his wife and daughter. For the sake of this example, assume that the wife is listed as the first victim entered on the incident-level record. For the offender extract, the victim-offender relationship is coded as "Wife." For the victim-level extract, this incident generates two victim records, one for the wife and one for the daughter. The victim-offender relationship code for victim 1 is "Wife" but the relationship between victim 2 (the daughter) and the offender is coded as "unknown" in this application. Note that a small proportion of incidents involve multiple victims (5%, or 981 of 18,464 incidents in 2020).

Modifications to the FBI's Data File

The underlying data structure of the raw SHR as compiled by the FBI permits up to eleven victims and eleven offenders to be placed on each incident record. In those rare instances where a crime results in more than eleven homicides, the victim information is spread over more than one record, with the offender information repeated on each. Without extraordinary knowledge of the incident, an analyst is unable to determine from the data file alone when separate records involve the same offenders.

In April, 1995, an explosion at the Federal Building in Oklahoma City killed 168 individuals. At the time information was reported to the Supplementary Homicide Reporting Program, law enforcement believed three offenders were responsible for this act. Following reporting guidelines, the information on this incident in the FBI's 1995 SHR data file was spread over 16 records (15 containing 11 victims and the last containing 3 victims) with 3 offenders noted on each record. Without extraordinary knowledge of this incident, an analysis of these records would yield 168 victims and 48 offenders. The data files underlying this analysis package have been adjusted to accurately reflect an incident with 168 victims and 3 offenders.

The Oklahoma City incident is only one of several occurrences in the SHR data of incidents with more than 11 victims. Work has been initiated to develop the background information on similar incidents so that they can be accurately reported in future Easy Access packages.

Data Reduction

From these master files, two analysis files were created to reduce the complexity of the data structure so that it could be processed efficiently with this application. The first task was to recode information on the weapon used and the victim-offender relationship into a smaller set of coding categories. The original codes from the SHR file were grouped as follows:

Victim-Offender Relationship

• Family - Husband, Wife, Common-law husband, Common-law wife, Mother, Father, Son, Daughter, Brother, Sister, In-law, Stepfather, Stepmother, Stepson, Stepdaughter, and Other family member.
• Acquaintance - Acquaintance, Boyfriend, Girlfriend, Ex-husband, Ex-wife, Employee, Employer, Friend, Homosexual relation, Neighbor, and Other known individual.
• Stranger - Stranger.
• Unknown - Relationship unknown.

Weapon Used

• Firearm - Firearm, Handgun, Rifle, Shotgun, and Other gun.
• Knife - Knife, Cutting instrument, Icepick, Screwdriver, Axe, etc.
• Blunt object - Hammer, club, etc.
• Personal - Hands, Fists, Feet, and Other personal weapon.
• Other - Poison, Pushed out window, Explosives, Fire, Drugs, Drowning, Strangulation, Asphyxiation, and Other unknown weapon.

Weighting

The annual variations in the proportion of homicide incidents reported to the FBI could easily confuse any interpretation of the data if the analyses relied solely on reported data. Therefore, annual estimates had to be developed. Each year in its Crime in the United States series the FBI publishes estimates of the number of murder victims in the United States and in each State. These estimates are based on the SHR data and information about the nonreporting law enforcement agencies. Annual national weights were developed for the victim-level data file by dividing the number of estimated murder victims in a particular year (from the Crime in the United States series) by the number of murder victims in the SHR data file for that year. Using this procedure, the annual estimates of the number of murder victims as reported in the Crime in the United States series are replicated by this package. This procedure assumes that the reported data have similar characteristics and relationships to the unreported incidents. There is no way of assessing the validity of this assumption. This same national weight was also applied to each record in the offender-level file. The weighting of both victim and offender records assumes that if non-reporting agencies did report their data (including the pattern of known and unknown offender information), these data would be similar to that in the reported data.

Using the same approach, state-specific weights were developed for each year. These weights were based on the assumption that incidents reported by law enforcement agencies within a state were similar to those incidents not reported within the state. There was one exception to this weighting process. Some states did not report any data in some years. For example, Florida reported no incidents to the Supplementary Homicide Reporting Program for the years 1988 through 1991. In situations where a state reported no data for a complete year, no estimates were prepared. Additionally, when the reported data for a state is less than 50% of the FBI's estimate for that state in a particular year, no estimates are presented in this application. [the Data Coverage table below lists those States with incomplete data]. These instances are coded "**" in the state-specific data tables presented in this application. The annual national weights, however, attempt to compensate for those few instances where states do not report any data.

The National Center for Juvenile Justice prepared tables [.xls format] documenting for each state the number of homicide victims reported in the annual SHR data files along with the estimated number of homicide victims reported in the FBI's annual Crime in the United States reports.

Data Coverage

As noted in the section on Weighting, the data available in this application varies by State and year. For example, some States did not report any data to the Supplementary Homicide Reporting Program in some years. Additionally, the reported data from some States is substantially below (i.e., less than 50%) the FBI's estimate for a particular year. This application does not display estimates for States that did not report or were determined to underreport for a specific year. The table below lists those States (and data years) for which not all data are available in this application. States not shown in this table have data available for all years.

September 11, 2001 Terrorist Attacks

The source Supplementary Homicide Reports (SHR) data files include the incidents of the September 11, 2001 terrorist attacks on New York, New York (the World Trade Center), Arlington, Virginia (the Pentagon), and Somerset County, Pennsylvania. These records are not included in this web application. The FBI prepared a special report on the victims of these attacks in Section V of the Crime in the United States 2001 publication.