Standardizing the Display of IBR Data:
Time and Date Variables
Data Collection and Quality Issues Associated with Time and Date Variables
Time and Date at a Glance
|Required?||Time and Date, but not Hour|
|Number of Entries?||1|
|Coding Options?||Hour is broken into 1 hour categories using military 24-hour time.|
According to the FBI Data Collection Guidelines, the incident date/hour variable represents the month, day, year, and hour when the incident occurred or started, or the beginning of a time period, if appropriate. Military 24-hour time is to be used. If the incident date is unknown, the date of the report is entered, with the indicator 'R'. If the incident hour is unknown, the hour is left blank. An hour category includes all offenses occurring in that hour. For example, if the incident occurred on or between 4 pm and 4:59 pm, '16' is entered. If the incident occurred at exactly midnight, it is to be considered to have occurred at the beginning of the next day, as if the crime occurred at 1 minute past midnight.
The "Concept of Time and Place" is also used in NIBRS. In other words, if more than one crime was committed by the same person or group of persons and the time and space intervals separating them were insignificant, all of the crimes make up a single incident. In the Summary system, the concept is used to determine whether the Hierarchy Rule is to be applied to a group of crimes; and if so, the crime which is the highest in the hierarchy is the only one reported.
In NIBRS, although the Hierarchy Rule is not used, the concept of time and place is still applied to determine whether a group of crimes constitute a single incident. This is of crucial importance since the application of the concept will determine whether the crimes are to be reported as individual incidents or as a single incident comprised of multiple offenses. Because of the emphasis in NIBRS on reporting all of the crimes involved in an incident, additional information may be helpful.
An INCIDENT is defined as one or more offenses committed by the same offender, or group of offenders acting in concert at the same time and place. SAME TIME AND PLACE means that the time interval between the offenses and the distance between the locations where they occurred were insignificant. Normally, the offenses must have occurred during an unbroken time duration and at the same or adjoining location(s). However, incidents can also be comprised of offenses which by their nature involve continuing criminal activity by the same offender(s) at different times and places, as long as the activity is deemed to constitute a single criminal transaction.
Data Quality Issues
Zero, which is supposed to represent the midnight hour, might be mistakenly used to report missing or unknown data. This may be due to software defaults, which may enter "0" when no hour is reported. The FBI does not screen submissions for this coding error. As a result, your data set may have an unusually large number of offenses occurring at midnight. In the 1999 NIBRS data, for example, a frequency of incident hour shows that 8.5% of all incidents are coded as midnight. However, at 11pm, only 4.9% of incidents are occurring, and at 1am, 3.3% are occurring. This suggests that some incidents coded as midnight should have been coded as unknown.
A better way of looking at this trend is to use a line graph. The graph on the left shows the frequency of incident hours, including midnight. The sharp peak at midnight does not seem to match the flow of the line, indicating a coding error. The graph on the right shows the same data, but without the incidents coded as zero. The ends of the line are approaching each other, suggesting that the true number of incidents occurring at midnight probably falls between 70,000 and 100,000, rather than the 174,000 reported.
For an example of some alternatives for recoding the incident hour for use in analyses, see the Data Quality Section.