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Crime rate calculation method due for overhaul, Wayne State University researchers say

April 10, 2013
David Merolla, Ph.D.
Zavin Nazaretian

DETROIT — A technique for calculating criminal incidence rates significantly underestimates the number of crimes — especially the violent kinds — that occur in Canada, two Wayne State University researchers believe.

In a study published recently in the Canadian Journal of Criminology and Criminal Justice, WSU Ph.D. student Zavin Nazaretian and David M. Merolla, Ph.D., assistant professor of sociology in the College of Liberal Arts and Sciences, found that a method called “capping” — which only allows survey respondents to represent a maximum of three incidents per crime type regardless of how many incidents they report — undercounted violent crime by 87 percent and household crime by 36 percent.

Capping is a common methodological practice used in most victimization surveys. The researchers don’t believe it is a deliberate attempt by governments to mislead, but rather a once-useful practice that must be rethought in order to yield more accurate crime reporting. Capping has been used to try to correct response bias by limiting the number of individual victimization incidents that one person can represent in official rates.

The study, “Questioning Canadian Criminal Incidence Rates: A Re-analysis of the 2004 Canadian Victimization Survey,” examined seven of the eight personal or property crime categories from that survey, which sampled 23,700 households. Nazaretian and Merolla found substantial differences in how household and violent crimes are affected by capping, with results indicating that violent crime is much more sensitive to capping techniques than household victimization.

That pattern is consistent with research on repeat victimization, and indicates that individuals reporting more than three victimizations likely are providing accurate responses.

“By capping the numbers, some crime types increase more than others, possibly making the distribution between property crime and violent crime seem more comparable,” Nazaretian said. “Perhaps that translates into spending more money on protecting vehicles that could instead be used to support things like homes for battered women.”

“We argue that the increase is so much more for violent crimes, it’s likely that at least some of these high numbers are real criminal events,” Merolla said. “Rather than limiting it to three, we should be working toward developing some sort of methods to better understand when a report is likely to not be verifiable, or when it’s likely to be a real crime.”

In the study, the researchers came up with new figures by including all incidences actually reported, leading to much different conclusions for some crimes. For example, Nazaretian and Merolla said the rates barely changed for vehicle theft, but increased for assault by 90 percent, from 51 incidents per 1,000 adults to 96.

“This shows, even when using its own numbers, that crime, particularly the most egregious types, is possibly much higher than the government reports,” Nazaretian said.
The researchers believe the higher numbers also provide insight into the number of unreported crimes when compared with arrest rates reported by police agencies, and that the cost of crime likely is more than is being reported.

The researchers said their report is not intended as a criticism of Statistics Canada, the agency that conducted the survey, but rather as evidence of the need to update a statistical technique for policy reasons and better resource allocation.


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Wayne State University is one of the nation’s pre-eminent public research universities in an urban setting. Through its multidisciplinary approach to research and education, and its ongoing collaboration with government, industry and other institutions, the university seeks to enhance economic growth and improve the quality of life in the city of Detroit, state of Michigan and throughout the world. For more information about research at Wayne State University, visit http://www.research.wayne.edu.