The Slashdot forum managers have approved yet another troll message: In Cameras Help Cops Catch a Killer, they ask whether or not the use of cameras to help catch a killer justifies the increasing use of surveillance in public spaces.

The answer is "no".

There are a couple of ways to think about this, and at least one of them points to a big flaw in the way we carry out public discourse.

First, let's consider the social implications. Suppose you say that surveillance is good, and we should install cameras everywhere, even in living rooms, bedrooms, and bathrooms. Wouldn't this prevent all crimes?! (No, it probably wouldn't; criminals adapt too, you know.) And, even if it did, privacy and solitude is a prized commodity: not something I want to yield on the off chance that it will solve a crime.

The more compelling argument IMO is to run the numbers. These arguments tend to focus on the "true positive" rate -- the number of crimes solved (sometimes spectacularly) by the use of the nifty tech -- but that's only 1 of four numbers you should consider. We also need to look at "true negatives" (how many innocent people are you surveilling?) "false negatives" (how many crimes are committed out of the reach of public surveillance?) and "false positives" (how many people are falsely accused based on misuse of the technology?) If most people don't commit crimes, then even if you catch all of the criminals, your false positive rate will dominate and you will have a lousy predictive ability. Likewise, if you have a high sensitivity to crimes committed in public, but most crimes are committed out of reach of public surveillance, you will have poor sensitivity and your false negatives will dominate.

This is where I think the flaw in our public discourse lies. When thinking about surveillance, SWAT teams, FAA regulations, DHS screening, etc., you have to ask yourself what signal you're looking for. If you're looking for one person in a million (a conservative estimate for passenger screening!) then you need a really sensitive filter if you're going to avoid hitting lots of false negatives, and you're going to have to have a really specific filter if you're going to avoid inconveniencing innocent people.

And, of course, there's always Bruce Schneier to point out that the Bad Guys adapt.

The only moderately intriguing (but also chilling) pro-surveillance argument that I have found is in David Brin's The Transparent Society, where he argues that the only way forward is to make the surveillance cameras publicly accessible. This would not only prevent crime but would also prevent police abuses of the technology.

A compelling counterargument to this can be found in Vernor Vinge's book A Deepness in the Sky. Vinge makes the essential point that in a transparent society, tyranny becomes an algorithmic challenge: he who extracts the most information from the surveillance technologies dominates. Not reassuring to me, thank you very much.

--titus

p.s. I am increasingly irritated at the adolescent phrasing of the posts that slashdot approves. One more reason to go readdit.

Legacy Comments

Posted by Ian Bicking on 2007-01-03 at 23:37.

The number of false positives is likely to be low.  Crime is generally
investigated when a person shows up missing, or someone claims to have
been the victim of a crime, or possibly when someone notices a crime
(maybe one where the victim can't speak on their own -- e.g., child
abuse -- or a victimless crime like drugs).  The point is that it
happens after the act.    This is very different from detecting
terrorist attempts, which have to happen before the act.      Also
including "true negatives" as a number isn't really fair -- it's up
for dispute if that number means anything at all.  If a picture is
taken of me, and no one ever sees it, have I lost anything?  Certainly
not.  If **maybe** someone sees me, have I lost anything?  Possibly;
it depends on a lot of what I'm doing, and what I think will happen
because someone sees me.  If **nothing** will happen, then the
negative effect is rather low -- not tiny, but not bad.  This is the
nature of public space now; as long as I can find **some** private
space, the proportion of private to public space is not so terribly
important.