The crime severity index: 1 murder = 300 assaults

There’s a big problem with the new scheme to count crimes in Canada. The country’s official number crunching agency, Statistics Canada, unveiled the crime severity index today. It’s the first serious revision to the country’s sanctioned, national crime tracking system in roughly half a century.

Intuitively, it seems like a good idea. Instead of just toting up the number of crimes reported to police annually and converting that into a rate per 100,000 people, we’re now going to count more serious crimes, like murder and sexual assault, a different way. Under the old scheme, one murder carried exactly the same weight in a community’s violent crime rate total as a common assault. In the new plan, one murder = 300 common assaults. One robbery = 20 mischief charges. Every community ends up with a crime severity index that reflects not only the number of crimes, but the severity of crimes. There’s an overall index, a violent crime index and a non-violent crime index for each community.

And so here’s the big problem. Watch for media, commentators, even prominent members of police agencies, civilian oversight bodies, and others, to begin touting the indexes as a definitive indicator of community safety. A low index, relative to the national average, should mean it’s a safe community, right?

Wrong.

The indexes are still built on the same wobbly foundation as our historic crime counting system – they rely on police reported crime figures. We know from other surveys that sample tens of thousands of Canadians that most crimes are never reported to police. Huge numbers of minor crimes are never reported and large numbers of violent offences go undocumented. It’s estimated that 9 out of every 10 sexual assaults is never reported to police. A low crime severity index for a city might tell us only that serious crimes in that community aren’t coming to the attention of police, for a variety of reasons. If they’re undocumented and unsolved, would that make a city a more dangerous place, since no one is hunting perpetrators? Maybe. The bottom line: The new crime severity indexes tell us only something about the numbers we already have. Exactly what that is, still isn’t clear.

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Related post: The safety fallacy

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