Effect Measure

Once, long ago, I used to be in a radiology department in a famous hospital. I liked radiology quite a bit and even before becoming a doctor I worked in them. Later I did research on the kinds of errors radiologists make when they read x-rays. One of the errors that was extremely well known even 40 plus years ago (although that didn’t prevent it from being made with dismaying consistency up to and including today) was something called “satisfaction of search error.” In essence, it meant that once one abnormality was found on an x-ray, there was an increased chance of missing a second, unrelated one.

Radiologists have known about this for a long time, but apparently people in other fields haven’t. It’s not just medicine. It is plausible to think that any task involving searching through a constantly changing and complex cognitive field might also have this problem. Like screening luggage at the airport. According to a paper in press at the Journal of Experimental Psychology: Applied by Fleck, Samei and Mitroff, this is exactly what we can expect:

This new study examined whether that concept also applies to airport-security scans, and it seems that it does. In fact, the researchers found, the problem may be worse among luggage screeners because they are under more time pressure than radiologists. They write that scrutinizing luggage for toothpaste and hair gel may come “potentially at the expense of finding additional targets which may be better concealed and less frequent, such as scissors, box cutters, or pocketknives.”

The study was conducted using Duke University students and computer simulations. So it’s reasonable to ask whether trained airport-security personnel would fall victim to the satisfaction-of-search issue. But, according to the authors, previous research suggests that, no matter how much training you have, the problem persists.

Obviously there are valid reasons for being concerned about potential weapons disguised as everyday items. But there may be a cost to being too careful. (Tom Bartlett, Percolator Blog at The Chronicle for Higher Ed)

The hair gel/liquids restriction was stupid from day one, a typical case of Bruce Schneier’s “Security Theater.” It’s been obvious that much Security Theater hurts us by being costly, inconvenient and ineffective. Now it appears it can also make us less secure.

What will they think of next? NB: that’s not a rhetorical question.

Comments

  1. #1 Scott Simmons
    April 27, 2010

    Heh. This coincides with my anecdotal evidence … When I showed up too late for a flight a couple of years back to check my bags, I dragged the one I had intended to check (which was just a little bit too big for a carryon) over to security. They not only missed the size issue (which the annoyed flight attendant thought they should have caught, according to what she said after I boarded), but about half a dozen items that were clearly outside the security guidelines, including a large nail file. They did catch my canister of shaving gel. “You can’t bring this on the plane,” the TSA screener told me, frowning. “Oh, OK–just throw it away, then,” I responded, waiting to hear the rest of the list of things I couldn’t take. Nope–that was it. They’d caught the forbidden gel, so their job was done, evidently … I decided not to try to hijack the aircraft with my nail file, toenail clippers, or shampoo.

  2. #2 James Davis
    April 27, 2010

    It’s a shame that basic science like this will probably be ignored in favour of throwing more regulations at the problem.

  3. #3 simba
    April 27, 2010

    This happened to me when I brought the wrong bag to the airport. The shampoo was taken, the penknife and the conditioner weren’t found.

  4. #4 RGS
    April 27, 2010

    I’ve used the same principle to hide an empty magnetic keyholder in an obvious position, while the one with the key was much better hidden.

    Regarding forbidden items: my wife had to throw out an unopened single-serving container of yoghurt. I’ve no idea how this could be used as a weapon. It is probably more an indication that 50% of all people, including security personnel, are of below average intelligence.

  5. #5 John Galt
    April 27, 2010

    Revere- thank you for highlighting this study. Not only do we have diminishing marginal returns of the newer security regulations due to the low positive predictive value of screening all shoes and liquids/gels/aerosols, we are detecting these “threats” at the possible expense of real threats.

    RGS- I suspect you are too harsh on the security personnel. This is a systems problem, not a marker for individual intelligence. If TSA makes a rule that no liquids/gels/aerosols of greater than 3 oz can be carried on a plane, then security personnel have to carry out that rule.

    It’s like working with a moving company. I’ve heard friends tell of companies that shipped trash cans full of food waste for a cross-country move. It sounds stupid- why not just throw the garbage out? But professional movers have to work within the financial and legal realities of their trade: (a) The secret to packing really fast is to not think. If you stop to think about every item, you’re going to waste time deciding whether it’s trash or whether the owner really wants it, and time lost = money lost. (b) If you throw out what looks like garbage (even when it obviously is, like the Hefty bag of food scraps), then one day you’re going to have an owner say they had dropped their jewelry in the trash by mistake and now you are liable for the cost of the reported jewelry. Safer just to pack everything, and leave the owner to throw out their own garbage before you show up.

  6. #6 Rose Colored Glasses
    April 27, 2010

    Of course it’s all theatre. The object is to keep the flying unwashed frightened, timid, docile, and obedient.

    The rest of the flying public is never bothered by the TSA. If you’re a corporate honcho, nobody searches you or your luggage, and there is no waiting at the airport: the corporate jet waits for you, its engines warming up when the pilots are notified by your driver that your limousine has reached the airport.

    Sure, corporate jets would make excellent flying suicide bombs, but this is a risk we have to take — because important people cannot be troubled. Abuse is only for the underclass.

  7. #7 Roman
    April 28, 2010

    @If you’re a corporate honcho, nobody searches you or your luggage, and there is no waiting at the airport: the corporate jet waits for you, its engines warming up when the pilots are notified by your driver that your limousine has reached the airport.

    Hmm. My corporation’s honchos flew economy in 2008. Cost cutting measures.

  8. #8 pft
    April 28, 2010

    Rose Colored Glasses. You are right.

    Roman. So because your companies corporate honchos fly economy, you point exactly is what? Do you deny the existence of corporate jets used by corporate executives just because your corporation does not have one.

    I don’t say they should be subject to security checks, but the Bin Laden family for example may have a corporate jet in Saudi Arabia, if not I doubt they fly commercial when they come to the US, probably hire a charter, so… Not saying they are a threat even if OBL is, but you know….

    In the meantime the peasants will have to fly naked soon.

    Theater.

  9. #9 RobT
    April 29, 2010

    Security theatre struck me last year when heading over to New Zealand for some trout fishing and family holiday. My carry on had a small box of trout flies, size 12 nymphs to be exact, that I was told were a danger because they had sharp points, and would have to be confiscated before boarding.
    The image of me taking over the plane with a deadly 10mm fish hook struck my funnybone and I burst out laughing. Unfortunately the “security officer” thought I was laughing at him, and things went a bit pear shaped for awhile until they relented, and put the deadly weapons in a sealed pouch to be guarded by the flight crew until we landed.
    If you saw it in a movie, you wouldn’t believe it.