Rate by Year
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Comparing crime counts from different years can be misleading if the underlying population has changed over time. For example, imagine that burglary counts remained stable in a city while the number of households increased dramatically. We would probably interpret this as a positive indicator because crime did not go up despite there being more targets available (i.e., households). This example highlights the need to control for the “population at risk” when comparing offense counts from different time periods. The best way to do this is by converting raw counts into rates. To create a rate per 10,000 persons the number of crimes in a given year is divided by the “population at risk” for that year and then multiplied by 10,000. Although the ideal “population at risk” to use for residential burglaries would be households, these data are unfortunately not available every year. Instead, for the chart above we used annual estimates of Portland residents, data we obtained from the U.S. Census Bureau.
Residential burglary rates in Portland were at their highest in 1995, with 102 incidents reported per 10,000 residents. Burglaries declined steadily until 2001, when they increased to a second peak in 2004. After this rates fell again leveling off over the past four years at 45.5 per 10,000. Although recent years have seen a slight increase in the burglary rate, for example the rate rose 4.9% from 2010 to 2011, this increase pales in comparison to the overall 52.9% decrease we have seen from 1995 to 2011.