Rates by Year
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Comparing simple crime counts across two distinct time periods can be misleading if the underlying population has changed. Take for example a case where the crime count in a city stayed the same from one year to the next but the population increased considerably. We might interpret this as a positive indicator for the city because you would normally expect crimes to increase with more people. A way to address this concern is to convert crime counts into crime rates, which control for population changes. Rates also tell us something about the risk people face or the likelihood of any one individual being victimized. To create a rate per 10,000 persons the number of crimes in a given year is divided by the population for that year and then multiplied by 10,000.
Street Robbery rates in Portland were at their highest in 1995, with 24.9 incidents reported per 10,000 residents. Street robberies steadily declined down to 11.5 per 10,000 in 1999. Similar to the pattern for counts, street robbery rates remained stable between 1999 and 2008 fluctuating between 9.7 and 12.4 incidents per 10,000. In 2009 and 2010 robbery rates declined further to 8.3 per 10,000 persons. Between 1995 and 2010 the street robbery rates in Portland have declined by 67%.