Occurrence date

Occurrence date is the date an event happened, or the date recorded as representing when it happened. It differs from when the event was reported and when the record became public. Some events have an uncertain or extended time range, so the field's definition and precision matter.

Choose the date that matches the question

San Francisco's police-incident dictionary distinguishes the incident date and time from the date and time the report was filed. That local distinction illustrates why a dataset can contain more than one legitimate date for the same incident. DataSF incident-report field definitions.

A chart grouped by occurrence date asks when the recorded events took place. A chart grouped by report date asks when they were reported. The totals for a particular month can differ even when both charts use the same records.

Example

Hypothetical: A resident discovers a bicycle missing on May 2 and reports that it was last seen late on April 30. The source record contains an occurrence range crossing the month boundary and a report date of May 2.

An analyst cannot assume the bicycle disappeared on May 2 merely because that is the report date. Nor should the analyst choose an exact April date without following the source's rule for uncertain ranges. The publication needs to explain which occurrence field or assignment method it uses.

Common confusion

Occurrence date is not always the date a call was created in a dispatch system. A call can report an earlier event. Conversely, an ongoing event may be reported while it is happening.

It is also not the date of arrest, case closure, or public release. Using one of those dates in place of occurrence changes the meaning of the timeline.

An exact-looking timestamp can reflect a recording convention rather than known precision. Check documentation before treating a default midnight value as evidence that the event happened at midnight.

Why recent periods can change

Records reported later can add to earlier occurrence periods. As a result, a chart's newest days may be less complete than its older days. CDC's explanation of reporting delays demonstrates this general timing issue in public-health data: event dates and report dates need to be tracked separately. CDC reporting-delay explanation.

For comparisons, use the same date basis and preserve the extraction date. A later download may contain additional information about the same historical period, changing its total without changing when the events actually occurred.

Related terms

• Report date
• Publication date
• Reporting lag
• Backfill

Sources

• San Francisco Police Department/DataSF: Incident Report dataset explainer, field definitions (revised March 2023) — Separates incident timing from report filing.
• CDC: Behind the Model—Nowcasting, January 30, 2026 — Explains event/report timing and incomplete recent observations; cited for the timing principle, not a police reporting method.