Statistics of crime reports is explained
- pottstownmercury
- Mar 9, 2015
- 2 min read
By Evan Brandt
Comparing crime in Pottstown to other locations requires calculating a “rate,” so that communities with different populations can be more accurately measured — an “apples to apples” comparison, if you will.
FBI crime statistics use a standard crime “per 100,000” calculation to come up with a rate.
So with Pottstown having one murder in 2012, with a projected population of 22,546, its murder rate is 4.4 per 100,000. In other words, if Pottstown had a population of 100,000 people, a statistician would expect to see 4.4 murders.
The chart comparing Pottstown’s crime “rates” in 2012, the last year rates are available, with Phoenixville, Coatesville, Norristown and Reading is called an “unadjusted table,” according to Marc Scott, associate professor of applied statistics at New York University.
“By using the same year for each town, you’ve controlled for secular differences. In terms of an accurate picture of those towns in that year, I think you can have a fair amount of confidence,” Scott said.
“But I would not draw too many conclusions for any of these towns based on a single year’s worth of data,” Scott warned. “One year does not a trend make. It needs to be buttressed by prior history.”
That warning was borne out by Chester County District Attorney Tom Hogan, who said Coatesville’s murder rate in 2012 is “a bit of an anomaly” due to disorganization of the police department there.
There were indeed six murders that year, but he pointed out that since changes were made in the police department, Coatesville has not had a single murder since 2012.
Similarly, Berks County District Attorney John Adams said violent crime in Reading has dropped “significantly” since 2012 due to aggressive anti-drug enforcement.
When looking at these comparisons, it is also important to consider that the FBI statistics on which they are based are “self-reported” by the thousands of police agencies across the country, creating a possibility for variation in reporting.
According to Stephen G. Fischer Jr., Chief of Multimedia Productions for the FBI’s Criminal Justice Information Services Division, the FBI exerts what control it can to ensure consistency in its statistics.
“To ensure these data are uniformly reported, the FBI provides contributing law enforcement agencies with a handbook that explains how to classify and score offenses and provides uniform crime offense definitions,” Fischer wrote in an e-mail to The Mercury.
“The FBI checks the quality of the data submitted to the (Uniform Crime Report) Program. Staff review the data to determine adherence to UCR policy, conformance to UCR definitions and principles, and consistency with established statistical methodologies and norms,” he wrote “ If errors or anomalies are found, verification and/or corrections are obtained from the submitting agency/state UCR Program.”
