Can we screen more efficiently?

David Frum asks: If dynamic concentration is good for criminals, why not for terrorists? Ans. Because there was no squeegee-artist or turnstile-jumper collective trying to outwit the police.

David Frum proposes that the same logic of concentration that I want to apply to law enforcement ought to be used in counter-terrorism programs such as air passenger screening. That turns out to be a lot trickier than it might have looked at first glance.

Footnote I hadn’t talked with Frum before, or read much of his work, but we had a very pleasant wonk-to-wonk chat. It’s not often that someone who has a bright idea is willing to listen closely to an argument about why it probably won’t work.

Author: Mark Kleiman

Professor of Public Policy at the NYU Marron Institute for Urban Management and editor of the Journal of Drug Policy Analysis. Teaches about the methods of policy analysis about drug abuse control and crime control policy, working out the implications of two principles: that swift and certain sanctions don't have to be severe to be effective, and that well-designed threats usually don't have to be carried out. Books: Drugs and Drug Policy: What Everyone Needs to Know (with Jonathan Caulkins and Angela Hawken) When Brute Force Fails: How to Have Less Crime and Less Punishment (Princeton, 2009; named one of the "books of the year" by The Economist Against Excess: Drug Policy for Results (Basic, 1993) Marijuana: Costs of Abuse, Costs of Control (Greenwood, 1989) UCLA Homepage Curriculum Vitae Contact:

4 thoughts on “Can we screen more efficiently?”

  1. You can't really apply dynamic concentration to airline screening because the costs don't depend on the violation rate: the vast majority of the cost is spent screening innocent passengers, and you're going to have to keep paying that cost no matter how low you drive the rate of terrorism among the targeted group. Dynamic concentration depends on the costs dropping as the violation rate is reduced, which allows you to devote more resources elsewhere.

    Dynamic concentration also depends on the fact enforcement can be reactive (since it involves deterrence by a threat of punishment, not the physical prevention misdeeds). That means that you can prevent the first targeted group from committing crimes after you've shifted your focus elsewhere since members of that group are dissuaded by your threat to investigate & punish them if they start acting up. That doesn't work with terrorism – if you shift your focus away from a group then a member of that group can slip through and commit an act of terrorism, and they won't be deterred by your threats of what you'll do afterward.

  2. I have a question about the screening system. Is Frum proposing the establishment of a massive, permanent data base of information about "secure travelers" whereby the screening questionnaire is filled out in advance, the answers are checked against credit history, USPS records, social security databases, etc. to insure their accuracy? Or does he propose that every traveler fills out the questionnaire which is then check between the time the ticket is purchased and the plane leaves?

    Or does he propose that we simply have everybody fill out the form and assume that terrorist won’t lie to us for basically the same reasons that Communists couldn’t take a loyalty oath?

    I don’t have any way to analyze the reasonableness of Frum’s thinking without knowing which of these alternatives he is proposing. This really does seem to combine the worst of “security theater” with a civil liberties/privacy nightmare of staggering proportions.

  3. Good article, reasonable opinions mixed with real, useful data. Though, like the previous commenter and many, many other people, I am wary of databases, aggregation, etc.; but that's an argument worth having. As to Mr. Frum, he really does seem to be competing with Reihan Salam for the title of "the most reasonable conservative pundit" award. Don't get me wrong, I'm pretty far to the left, and I thinks he's dead wrong about a whole host things. Beyond that he writes rather well: economical (short) and clear.

  4. It's interesting that he seems to respond to explanations of why screening won't really help with "but if we do a lot more screening, and it's really good…" It's the touching faith of someone who doesn't think they could ever be a false positive.

    What's interesting — and a little sad — about the data-aggregation issue is that it's an almost perfect application for the cryptographic zero-knowledge proofs techniques that have been floating around for the past 20-odd years. No one who knows passengers' names needs to know any of the data one which the security decisions are made; they just have to know whether to let someone through or hold them for additional screening of some degree. With the right protocol, each separate database could supply its stuff to a combining algorithm that wouldn't know the passenger's name either. With the necessary inclusion of some level of random screening, you'd get a system that would be hard to spoof without letting hundreds of millions of sensitive dossiers out into the world. (Yes, there are attacks on this kind of system, and countermeasures for the attacks, and so forth. But compared to either doing nothing or aggregating the information in one huge high-value target, it still seems like an idea worth pursuing.)

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