The Pomona College student who was detained by airport security after they found Arabic flashcards in his carry-on luggage was originally pulled aside for questioning because of Screening Passengers by Observation Technique (SPOT), a pseudo-scientific program that's supposed to teach TSA employees how to identify deceptive or hostile behavior in travelers.
Or, rather, SPOT is supposed to help pick out people who are trying to hide their cruel intentions. The pushy, cranky guy behind you in line who's yelling at his kid = no. Sneaky terrorists trying to look innocent = yes.
The problem, of course, is that there's no evidence this system works any better than a lie detector. Which, just to be perfectly clear, means it doesn't work.
"Simply put, people (including professional lie-catchers with extensive experience of assessing veracity) would achieve similar hit rates if they flipped a coin," noted a 2007 report1 from a committee of credibility-assessment experts who reviewed research on portal screening. "No scientific evidence exists to support the detection or inference of future behaviour, including intent," declares a 2008 report prepared by the JASON defence advisory group.
The TSA does track statistics. From the SPOT programme's first phase, from January 2006 through to November 2009, according to the agency, behaviour-detection officers referred more than 232,000 people for secondary screening, which involves closer inspection of bags and testing for explosives. The agency notes that the vast majority of those subjected to that extra inspection continued on their travels with no further delays. But 1,710 were arrested, which the TSA cites as evidence for the programme's effectiveness. Critics, however, note that these statistics mean that fewer than 1% of the referrals actually lead to an arrest, and those arrests are overwhelmingly for criminal activities, such as outstanding warrants, completely unrelated to terrorism.
I'm in favor of reasonable security measures at airports. But, from my perspective, a big part of defining "reasonable" is providing objective evidence that the measure actually does any good.