Standardizing the Display of IBR Data:
Weapon Variables

Frequencies of Reported Weapons

The 1999 NIBRS file contains 2,314,396 offenses from 18 states.  All of the possible weapon types occur in the file.  The frequencies for each weapon type (for the first weapon variable only) are presented below.

Of the reported offenses, 17.5% involved a weapon; 1.6% of the offenses included the use of a firearm.  Personal weapons (hands, fists, feet) are the most common weapon used, with 12.2% of the offenses involving this category. 

Despite there being a category for "None", 79.7% of the incidents are missing an entry for weapon type.  These most likely represent offenses that do not require weapon offenses, and can be checked by looking at only the violent offenses. 

Frequencies of Reported Weapons for Violent Offenses

When only violent offenses (murder and nonnegligent manslaughter, forcible rape, robbery, and aggravated assault) are selected, 92% of the cases involve a weapon.   Surprisingly, 8% still report that no weapon was involved, despite the violent nature (and coding rules) of the reported offenses.  There are 115,784 violent offenses, and the most frequent weapon is again personal weapons, with 31.1% involving hands, fists, or feet.  Firearms are used in 19.1% of the offenses, most commonly a handgun.  Weapon type is unknown in 3.5% of the offenses.

Since weapon type is required for these offenses, there are no missing data for this variable.

Number of Reported Weapons per Offense

Part of the advantage of NIBRS is the ability to capture a wealth of information; it is possible to report up to three weapons in NIBRS.  The table below presents the number of weapons involved in offenses that reported the use of a weapon.   As the table shows, either very few offenses involve multiple weapons or these weapons are not being reported.

Use of Automatic Weapons

Automatic weapons are also reported in the 1999 data file.  Of the 36,811 offenses reporting the use of at least one firearm, 7.8% of involved at least one automatic weapon.  Note that the number of offenses involving a firearm is larger than the number of violent offenses reporting the use of a firearm.  Most of these additional offenses are weapons violations and kidnappings.