The risk of queuing?

As of the 23rd May 2022 this website is archived and will receive no further updates. was produced by the Winton programme for the public understanding of risk based in the Statistical Laboratory in the University of Cambridge. The aim was to help improve the way that uncertainty and risk are discussed in society, and show how probability and statistics can be both useful and entertaining.

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You’re finally landed after a nightmare flight in cattle-class. All you can think of is getting home, cleaning up the cat-sick and opening the post and a bottle of wine. Then you get to immigration control and are confronted by a queue that overflows the room, with a patient border official steadily working their way through the grumpy mob. It’s enough to make you want to stay at home.

I have developed an intense dislike of flying due to the deep unpleasantness of ‘the airport experience’, and offer a hug to anyone who is prepared to try and improve it. Which is why I have some sympathy for the UK Border Agency staff who have been suspended because they apparently sanctioned a slackening of immigration checks down to ‘Level 2’ over the summer when queues got too long. Melanie Phillips in the Daily Mail is shocked that terrorists may have been let into Britain because ‘a few airline passengers are moaning about delays’, and I have certainly moaned about under-staffing at border controls. But were we really exposed to increased risk of terrorism?

This would not be difficult to establish. The standard checks must have a known yield of suspects, wanted criminals, pseudo ‘students’ and so on. Provided the Level 2 regime was used at unpredictable times, then the numbers of such people trying to get into Britain would be unaffected, and so we can compare how many were caught under Level 2 (probably not many) with how many would be expected to be caught normally (possibly not many more).

The point is that security checks operate as much as a disincentive as to detect individuals at the time. Which is why they can be used on a random basis – if a baddy knows there is a reasonable chance of being caught then he may think again. So not everyone has to be tested equally, provided it is genuinely unpredictable who will be taken aside. Of course it would be different if it were known that some airports had permanently lax security – that could be seriously dangerous.

I don’t know the details of the Border Agencies procedures, but they seem to have either operated either a full screen, or very little. With my statistician’s hat on, I would recommend they install a little flashing device in each booth that signals at random when someone should be examined in detail. Crucially, the rate of people being selected for full scrutiny can be varied according to the queue.

Security costs more than the wages of the inspectors. The annoyance and missed trains of returning Brits is one thing, but more important is the image of this country held by bona fide foreign visitors and businessmen - personal experience suggests the current visa regime is seriously damaging international collaborations. Someone should work out the cost-effectiveness of keeping queues short.

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