The profiling of behavioral cues to identify terrorists is the latest trend in American airport security. The Transportation Security Administration began experimenting with the technique last December at a dozen airports, and after this month's reported bomb plot in Britain, agency officials said they wanted to train and redeploy hundreds of routine screeners at airports across the nation by the end of next year.
There's no question we'd all like to improve airport security. But investing heavily in seemingly high-tech methods like behavioral profiling isn't the answer, and may make air travel less safe on the whole.
To understand why, consider that just a few days after the introduction of stringent carry-on limits following the British bomb scare, a 59-year-old woman from Vermont boarded a Washington-bound jet at London Heathrow Airport, became unruly, and caused the plane to be diverted to Boston. A careful search discovered that she'd brought on the plane several cigarette lighters, matches, a screwdriver, hand lotion and bottled liquids.
How she managed to get those items through heightened screening is still unclear. What is clear, though, is that this passenger helped expose the Achilles' heel in airport security: the basic search.
Behavioral profiling -- especially the cut-rate version the T.S.A. has in store for us -- is not going to help in this respect. Learning to defeat poorly trained screeners is a lot easier than learning to fly a jumbo jet. The likely result is that our newly minted behavioral detectives will be singling out and searching the wrong passengers.
Behavioral profiling is by no means new. In the mid-1960's, Paul Ekman, a professor at the University of California at San Francisco, began researching how facial muscle movement relates to emotions. He noted several thousand facial muscle combinations and put together the Facial Action Coding System -- an intricate, 500-page catalog of facial expressions.
Since then, there have been many studies of the ability to detect truth and deception, but they have been largely disappointing. A review of the literature published in 2000 found that in experiments where subjects were trying to detect whether others were telling the truth or lying, the subjects had an overall success rate of 56.6 percent -- slightly better than a coin toss. In the studies that broke down their data, it was found that subjects were able to determine that they were being lied to only 44 percent of the time -- meaning that they would have done better closing their eyes and guessing.
A few studies have found that certain elite, highly trained professional groups may beat chance under specific conditions; however, a comprehensive survey of those also concluded that their accuracy rates overall were unremarkable. As Dr. Ekman himself noted in 1999, almost all the studies ''have found that accuracy is close to chance.''
Some anecdotal evidence is becoming mythic, but it's largely misleading. The most common involves Ahmed Ressam, the millennium bomber, who was apprehended at the Canadian border in 1999 trying to smuggle bomb-making equipment. Mr. Ressam became a suspect when a customs agent felt that his itinerary seemed unusual and that he was acting oddly.
Many credit his arrest to a profiling plan put in effect by Raymond Kelly, then the head of United States Customs and now New York City's police commissioner. True, under Mr. Kelly, the Customs search success rate improved by 25 percent while the overall number of searches decreased by 75 percent. But his profile rested on six factors, only two of which were behavioral. The four other factors involved canine searches, incorrect or suspicious paperwork and specific intelligence or contraband implicating the suspect. It's unclear how much of the improved success turned on behavioral cues alone.
The remarkable track record of the security force at Ben-Gurion Airport near Tel Aviv -- no successful hijackings ever-- is also often chalked up to behavioral profiling, but that too is naive. For three decades, the airport has had intensive security practices and a sky marshal program. All departing passengers are interviewed and subjected to one-on-one searches that, according to Rafi Ron, former head of security at Ben-Gurion, take an average of 57 minutes per person.
Israel is thought to have had the most success with behavioral profiling. But again consider how the Israelis do it: they recruit their officers mostly from the military, subject them to stringent tests in order to weed out all but those with above-average intelligence and particularly strong personality types, and give them nine weeks of training in behavior recognition.
This is a far cry from the T.S.A.'s program: recruits are routine screeners, required only to have a high school degree and a criminal background check; they are given four days of classroom training in observation and questioning techniques, three days of field practice, then sent out on the job.
Rather than divert hundreds of screeners and untold dollars to high-tech fantasies, we need to invest those resources in hiring more routine screeners and giving them better training in basic searches.
If we want to change the system, a better idea would be to eliminate most carry-ons and emulate high-security prisons. In my experience, most prisons operate the same way: first I check my briefcase, overcoat, belt, cellphone and all unnecessary items at the reception. I then take everything out of my pockets -- wallet, pen and paper. A guard conducts a thorough pat-down search and physically inspects my property and shoes. We're done in less than a minute.
Sure, this would not be 100 percent foolproof. But, in combination with our sky marshal program, it would be far more likely to prevent future terrorist hijackings than giving a bunch of unqualified screeners a cursory education in face reading.
Bernard E. Harcourt, a law professor at the University of Chicago, is the author of the forthcoming Against Prediction: Profiling, Policing and Punishing in an Actuarial Age.
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