Thursday, April 21, 2005

London Violent Crime Still on the Rise

Apparently up 10% in the last year. But the Politicians have a reason for that:
But ministers also insisted that the apparent increase in violence is due to changes in the way crime is recorded. Labour pointed to evidence from the British Crime Survey (BCS), a giant opinion poll, that violent crime has actually declined. [Emphasis Mine]

I am not a fan of victimization surveys. Though the author of the survey has this to say.

Professor Hough told the Standard: "Police statistics in the Met show a rise in violent crime since 1997.

"But this is almost certainly an artificial rise, caused by large changes in the way the police record crime. The BCS is a better guide to crime trends in London and, according to that, violent crime in London fell in the five years from 1997 - though there are now some signs that the trend is reversing."

Is this an increase that can be associated with police actually accurately reporting crime? Or is the BCS not really an opinion poll? Last I knew the BCS was a vicitmization "survey," which makes me very certain it is based on opinion. I don't understand how an opinion based study can be used to rate the level of crime. How do people's perceptions make for scientific data?

I can't presently find it, but I believe that the reporting of crime in England has changed since 1997. From what I recall they used to report a single crime based on the perpretrator and not based on the number of times he did it. Say a single mugger beat up 5 old ladies, that would have been reported as a single mugging. I'm having troubles finding out exactly when the reporting methods changed, but I'll keep looking.

Here is a site that looks at this Home Office Crime report compared to the BCS.
The answer lies in the difference between two different ways crime can be measured. The BCS is a victimization survey. It is conducted by asking a sample of the population questions about any crimes they might have experienced. The other way crime is measured is being collating crimes reported to the police. Because most crime is not reported to the police, surveys like BCS give a much more accurate estimate of the total number of crimes than police reports.
I'm not certain I totally agree with this. I've seen several analysis of these victimzation surveys and they conclude that generally the surveys over report victimization for various reasons. Usually the over-reporting inaccuracy may be related to the strong emotions of the victim. Under-reports are attributed to embarassment or shame. This is pretty much a simplification of the topic that has a lot of depth. You can find various discussions on the topic fairly easily online.

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