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Reliance on raw statistics makes city crime rankings misleading: analyses should consider uncertainties, criminologists say.

Overconfidence in crime statistics doesn't pay.

In a new study, a team of criminologists makes the case that reported crime rates should acknowledge uncertainty in the data. The research demonstrates that rankings of cities as safer or more dangerous- which can influence tourism and tax spending--can be highly misleading.

"If you look at crime rates from year to year and you see a change, there's a fundamental ambiguity in whether that change is caused by a real change in crime, a change in reporting or some of both," says criminologist Robert Brame of the University of North Carolina at Charlotte, a coauthor of the new study. "Our position is we should own that. There's ambiguity here and we should learn to deal with it."

To get a sense of that ambiguity, Brame and his colleagues calculated the wiggle room in burglary data for the 10 biggest cities in North Carolina for 2009 and 2010. Based on state population estimates and the residential burglaries reported by police departments, the standard simple calculation suggests that in 2009 Wilmington had a higher residential burglary rate than Charlotte, for example. But when the researchers included known uncertainties in the numbers, Charlotte was too close to Wilmington to discern if one really had a lower or higher burglary rate than the other. Ambiguity in the data also meant that the researchers couldn't tell if the rate of burglaries in, say, Raleigh and Winston-Salem had dropped or risen from 2009 to 2010. Brame, University of North Carolina colleague Michael Turner and Raymond Paternoster of the University of Maryland in College Park reported their analysis online April 30 at

A major source of uncertainty lies in how many crimes are actually reported. Researchers investigated the issue using two sources of data: hard numbers of reported crimes and estimates of how many crimes go unreported. The hard numbers came from state data compiled for the FBI's Uniform Crime Reports. For residential burglaries, these numbers are known to be underestimates: If a burglary occurs along with a more serious crime, such as aggravated assault, rape or murder, the incident will be recorded as the higher-ranking offense.

For estimates of unreported burglaries, the researchers turned to the National Crime Victimization Survey of the Bureau of Justice Statistics, which compiles yearly data from interviews with roughly 40,000 households on their experience with crime and whether they reported crimes they encountered.

The NCVS survey data suggest that the national rate at which residential burglaries are reported to the police varies, but has increased in recent years. In 1999, for example, 49.3 percent of victims said the crime had been reported. In 2009, 57.3 percent of burglary victims said the event had been reported, and in 2010, 58.8 percent did.

A major factor affecting these numbers is a community's perception of and relationship to the law, says sociologist David Kirk of the University of Texas at Austin. Some communities perceive the police as helpful; others see the police as out to get them. This means that more crimes might be reported in a community that trusts its police department, giving the impression that the community has more crime.

Using the data on burglaries that go unreported, Brame and colleagues gave their estimates an upper and lower bound. They also accounted for uncertainty in city size, since population estimates by states often differ from federal numbers. The researchers argue that presenting crime data as an interval offers more meaningful information about whether a particular crime intervention strategy or youth education program is working, even if the answer is "we don't know."

Criminologist Richard Rosenfeld of the University of Missouri in St. Louis, who has spent years studying crime trends, says more such studies are needed. Not only are the numbers often fuzzier than they appear, but within a city, crime varies greatly across neighborhoods. The best predictors of whether people are at risk for crime isn't the city they live in, says Rosenfeld, but factors such as age, gender and whether the person is involved in criminal activity.

49.3 percent

U.S. burglary victims saying they reported it, 1999

57.3 percent

U.S. burglary victims saying they reported it, 2009

58.8 percent

U.S. burglary victims saying they reported it, 2010

Keeping up with crime Using raw crime statistics to rank cities according to safety can give a false impression. Including the rate of unreported crimes and other measurable sources of error offers a fuller view, criminologists argue.



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Title Annotation:Science & Society
Author:Ehrenberg, Rachel
Publication:Science News
Geographic Code:1USA
Date:Jun 16, 2012
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