Thursday, May 15, 2008

Surveillance cameras and crime

Having written before about longitudinal research showing that, except for a handful of specific circumstances (like car parks), surveillance cameras don't reduce crime, I was interested to see a study described by the blog Judgement Day about camera use in Philadelphia, where researchers claimed cameras reduced crime in target areas by 13%.

That's a pretty startling claim of success that flies in the face of meta-research on the topic.

Examining the study itself (pdf) more closely, the topline summary of a 13% reduction based on the cameras looks pretty overstated. When you get down to the bottom line (see the chart at the bottom of page 11), researchers found crime did not go down overall at half the sites.

Researchers divided 18 cameras into 8 different sites because several were placed close to one another. Of those 8 sites, they found no crime reduction at four of them. At two sites, crime went down but increased just outside of camera range (one of the two, said researchers, had a net gain despite crime displacement). At only two of the sites did the cameras reduce crime, supposedly without displacing crime elsewhere.

That's a much more mixed set of results than the topline finding that crime declined 13%. And of course, only analyzing 8 sites for a short period of time, the Philadelphia study is analyzing a pretty small dataset. When the British Home Office looked at camera effectiveness in London (pdf), cameras were already in place much more ubiquitously, and could be analyzed over much longer periods of time.

Over at HowStuffWorks, Cristen Conger had this assessment of the overall body of research on the effectiveness of police cameras that I more or less agree with:

So taken as a whole, what do all these numbers mean? The Home Office Research Group conducted another more comprehensive study in 2005, confirming that CCTV networks appear nearly ineffective [source: Gill]. A similar evaluation from 2006 by the U.S. Department of Justice, also questioned the reported success of CCTV systems, finding little evidence that they significantly reduce crime [source: Ratcliffe].

This isn't to say that crime cameras are entirely useless. Evidence consistently points out that cameras reduce auto-related crimes as much as 41 percent [source: Welsh and Farrington]. They are also more helpful with reducing crime in enclosed areas with less foot traffic when combined with other law enforcement efforts. And they're helpful in conducting post-crime investigations [source: Ratcliffe].

Nevertheless, the 2005 Home Office study revealed that the cameras did not produce enough bang for the buck. Federal and state governments have poured millions into the set-up and upkeep of crime cameras, but the Home Office study revealed that they were underutilized and not fully integrated into police strategies [source: Gill].

That's a good summary of the current state of research on surveillance cameras' effectiveness. They're useful for some, specific purposes, but in general public spaces are more what Bruce Schneier refers to as "security theater," which is to say, not entirely useless but mostly for show.

Over the weekend I happened to listen online to a talk by Schneier in which he reminded his audience not to be entirely dismissive of security theater, but to understand it for what it is and not mistake it for real-world security; that's good advice for policymakers regarding surveillance cameras. There's good research out there (much of it cited above by Conger) about when and how cameras do and don't work to improve safety. Beyond those uses, surveillance cameras in public spaces are more about theatrics than security.


Fred said...

CHINA'S ALL-SEEING EYE U.S. Contractors Have Helped China Build a High-Tech Police State – and It's Ready for Export

Gritsforbreakfast said...

Aw, Fred, that's just wrong. I blame you, as the messenger. ;)

Oh wait, no, I actually blame the Pentagon for collaborating with totalitarian Communists to perfect Big Brother.

Just imagine what Roy Cohn, "Uncle Joe" McCarthy, Barry Goldwater Sidney Hook, and all the Commie-haters from Cold War era would think if they'd lived to see this news! Unreal.

John said...

This is off-topic, but with Grit's interest in problems of Texas law enforcement and prisons, I think him and his readers will be interested in these pointers.

It turns out that our huge incarceration rate doesn't have much to do with reducing the crime rate. The National Bureau of Economic Research (NBER) has a paper by Jessica Wolpaw Reyes which demonstrates that eliminating lead in gasoline was responsible for a 56% reduction in violent crime. Her paper is at Amherst, the following TinyURL in case readers are interested.

My source is J. Bradford DeLong's economic blog or in Tiny URL for interpretation.

DeLong couples this report with the work of Steve Leavitt, at the Univ of Chicago who argues that legalizing abortion is responsible for another 29% reduction in violent crime. For a summary of Leavitt's argument see

DeLong adds the percentages up to get 85% reduction in violent crime due to unleaded gas and legalized abortion together.

I'm not sure you can simply add percentages and get a valid number. In fact, you can't, so 85% is not valid arithmetic. But DeLong's larger point should be that incarceration for long terms is at best a minor cause for reduction of violent crime.

Just thought you all would be interested.

Anonymous said...

could it be that cctv is just a feel-good panacea for the populace?