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Time of Day/Day of Week

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A temporal pattern commonly reported for residential burglaries concerns time of day: prior reports suggest that most burglaries happen during daytime hours when residences are often unoccupied. We utilized an approach called weighted time span analysis to determine when burglaries happen in Portland. This approach is necessary because victims often do not know the exact time that they were burgled so officers report a “low” date/time as well as a “high” date/time for the offense. For example, someone might report that their home was burgled between 9:00am when they left home and 12 noon when they returned home for lunch. For an offense like this it is difficult to decide which time should be used as the offense hour for an analysis: should you use the low time (9:00am), the high time (noon), or the time the offense was reported, say 1:00pm? Weighted time span analysis provides a solution to this problem by giving partial credit to each hour between the low and high times. For the event described above, 9:00am, 10:00am, 11:00am, and noon would each be assigned a weighted score of .25. A burglary that happened between 2:00pm and 3:00pm would assign a weight of .50 to 2:00pm and .50 to 3:00pm, and so forth. The weights are then added up for each hour in the clock and the distribution is graphed as shown above. For the current analysis we excluded incidents where the victim could not pinpoint the offense to a span of less than eight hours.

As shown in the chart above, Portland’s residential burglaries were grouped into two distinct periods: 1996 to 2003 and 2004 to 2011. Starting with the latter times, the red columns indicate that residential burglaries are much more likely during the daytime hours as compared to evening and nighttime. There also appears to be some shifting over the years with a higher risk in later morning hours for recent years as compared to 1996 to 2003 (blue line).

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Another temporal pattern in residential burglaries that has been consistently reported by researchers involves differences by day of week. Specifically, prior reports suggest that home burglaries are more likely to occur during the weekdays when residences are unoccupied. To assess whether this pattern holds true for Portland we examined data for 1996 through 2011, breaking the data into two distinct periods: 1996 to 2003 and 2004 to 2011. Here again we used a weighted time span analysis with low and high dates of occurrence. This approach used all cases when the police report was able to pinpoint the actual date of occurrence to within 2 days. The findings for this analysis are shown in the graph above with the earlier period, 1996 to 2003 depicted by the blue line and the period 2004 to 2011 shown in the red columns. Consistent with prior research, we found that offenses are slightly more likely to happen on weekdays as compared to weekends.

Overall, the data above indicate that burglars prefer to offend during daytime hours when residences are more likely to be unoccupied. This suggests that efforts by residents to make their home appear occupied when they are away could be an effective deterrent. Research suggests that vehicles parked in the driveway, the use of timed lights, and careful attention to other occupancy indicators (e.g., newspapers left out, garbage cans in street for several days, packages on door stoop) are effective strategies for dealing with this crime.