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GlossaryStatistics and interpretation

Incident count

An incident count measures distinct qualifying events. Learn why it differs from rows, calls, offenses, victims, and related report records.

An incident count is the number of distinct qualifying incidents in a defined dataset, area, and period. Its meaning depends on what the source calls an incident and which records it includes. Counting visible rows is valid only when each row represents exactly one qualifying incident.

Define the event before counting

For NIBRS, the incident concept links offenses involving the same offender or offenders acting together at the same time and place, subject to the program's instructions. One incident can contain multiple offenses, victims, and offenders. The FBI manual links these components through agency and incident identifiers. FBI NIBRS manual

A dispatch system may use a different operational event definition. Several calls from residents can concern one event, and an incident can generate several unit-response records. Police, fire, and medical systems may also create separate records concerning the same real-world occurrence.

This is why a cross-system total needs more than a shared address or approximate time. The analyst must determine whether the intended measure counts each system's records, each response, or deduplicated real-world events. Those are different legitimate questions with different methods.

Example

Hypothetical example: One police incident has two offense records and three linked victim records. A spreadsheet created by joining offenses to victims repeats the incident identifier across several rows.

The incident count remains one under the stated definition. The number of rows reflects the file's relationships, not additional events. If another agency uses the same numeric incident number, that number alone may not be unique across the combined dataset; the agency identifier is also needed.

Common confusion

An incident count is not an offense count. North Carolina's Justice Data Portal explicitly cautions that an incident can involve several offenses and people and that different counting units produce different figures. NC portal methodology

A supplemental report is also not automatically a new incident. It may add information to an existing case. Likewise, repeated public releases can include updated versions of the same record rather than newly occurring incidents.

Making a count reproducible

State the qualifying categories, date basis, geographic rule, identifier, and duplicate treatment. Decide how canceled, unfounded, or revised records are handled according to the source. A count for report date can differ from one for occurrence date. Preserve the extraction date as well, because delayed reports and corrections can change a previously published total without representing new events in that historical period.

Sources