The number of cleared crimes may be different from the number of arrests for many reasons:


1. Exceptionally Cleared crimes are included in the number of clearances.


2. The NIBRS Agency Crime Overview report allows the user to count arrests in two different ways: 
a) by when the incident took place 
b) or by when the arrest took place.  
This is one of the parameters at the top of the report.  If counting by arrest date, some arrests in a year can clear crimes that took place in the previous year. For example a report for 2021 can show cleared crimes that took place in 2020.  


3. The NIBRS Agency Crime Overview report displays number of crimes and not number of offenses. One incident can have multiple victims which means that a single offense can represent multiple crimes. This means that one arrest can clear multiple crimes.  In the image below, taken from a report based on the Offense Data cube, although there were 31 cleared Aggravated Assaults, this number comes from the fact that there are 31 victims, and these victims were spread across 24 different incidents.  Either there's a single incident with 8 victims, or multiple incidents had multiple victims in them.  A single arrest in any of these incidents would clear all crimes in the incident. 

4. In NIBRS, you can specify whether or not each arrestee should be counted, in order to allow for a single arrest to clear multiple incidents.  In the image below, taken from a report based on the Arrest Data cube, the 21 arrestees clearing Aggravated Assault are actually associated with 20 different incidents. There are also 4 incidents where the multiple arrestee indicator is set to "M", meaning that we won't count those arrests by default. The theory is that these arrestees are counted in other incidents. There is no way to verify this without an audit.


5. It is important to understand the distinction between the arrest offense and the cleared offense.  The arrest offense is the one stored in the arrestee segment and identifies a single offense for which the arrestee was charged.  The concept of a cleared offense is that all offenses in an incident are cleared by the one arrest.  For example, there may be an incident with a robbery, rape and aggravated assault for which two people were arrested, one for simple assault and the other for DUI.  This incident would show up in the report as cleared crimes (depending on the number of victims) in all three sections, but the arrestees would only be counted under the arrest offense. The image below , taken from a report based on the Arrest Data cube, shows that there was one arrest for Simple Assault that cleared at least one Aggravated Assault crime. 

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