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| Can statistics help catch terrorists? | Can statistics help catch terrorists? |
| (3 days later) | |
| In the wake of the alleged attempt to bomb a Detroit-bound plane, Britain could step up airport security with targeted passenger profiling. But how effective is it? | In the wake of the alleged attempt to bomb a Detroit-bound plane, Britain could step up airport security with targeted passenger profiling. But how effective is it? |
| The issue of passenger profiling can be controversial | The issue of passenger profiling can be controversial |
| Standing in a long queue at airport security with your fractious family, you might think it is pretty obvious you do not look like a terrorist. | Standing in a long queue at airport security with your fractious family, you might think it is pretty obvious you do not look like a terrorist. |
| But is your journey through security about to get easier - and your flight safer? | But is your journey through security about to get easier - and your flight safer? |
| The government says it is considering screening passengers to decide which should undergo more rigorous security checks. But the practice, known as passenger profiling, is controversial. | The government says it is considering screening passengers to decide which should undergo more rigorous security checks. But the practice, known as passenger profiling, is controversial. |
| People behaving suspiciously or with an unusual travel pattern might find themselves under additional scrutiny but racial or religious factors could also soon form part of the criteria. | People behaving suspiciously or with an unusual travel pattern might find themselves under additional scrutiny but racial or religious factors could also soon form part of the criteria. |
| But, in weighing up the merits of targeted versus random checks, the government will have to do its maths, because this seemingly straightforward idea is anything but in reality - not just because of fears that passengers will be unfairly discriminated against on grounds of ethnicity or religion, but because it involves some counter-intuitive number work. | But, in weighing up the merits of targeted versus random checks, the government will have to do its maths, because this seemingly straightforward idea is anything but in reality - not just because of fears that passengers will be unfairly discriminated against on grounds of ethnicity or religion, but because it involves some counter-intuitive number work. |
| For a start, in relying on who your statistics tell you is potentially high risk, your statistics could become unreliable, according to David Spiegelhalter, professor of the public understanding of risk at Cambridge University. | For a start, in relying on who your statistics tell you is potentially high risk, your statistics could become unreliable, according to David Spiegelhalter, professor of the public understanding of risk at Cambridge University. |
| FIND OUT MORE More or Less is on BBC Radio 4 on Fridays at 1330 GMT, and repeated Sunday 2000 GMTOr catch up on the iPlayer | FIND OUT MORE More or Less is on BBC Radio 4 on Fridays at 1330 GMT, and repeated Sunday 2000 GMTOr catch up on the iPlayer |
| "You're combating an intelligent adversary who could change their strategy in response to what you do," he says. | "You're combating an intelligent adversary who could change their strategy in response to what you do," he says. |
| To make sure your system is not predictable, any profiling strategy would have to be complemented by additional random checks across the whole passenger population. | To make sure your system is not predictable, any profiling strategy would have to be complemented by additional random checks across the whole passenger population. |
| "Game theory [an area of maths used, among other things, to predict and understand behaviour] shows that in response to an intelligent adversary, it often can be optimal to adopt a level of randomisation. | "Game theory [an area of maths used, among other things, to predict and understand behaviour] shows that in response to an intelligent adversary, it often can be optimal to adopt a level of randomisation. |
| "There must be an element where your computer says this individual must be examined carefully, whether it's a five-year-old child or a 90-year-old, so any opponent knows they might be examined no matter how little they seem to fit the risk profile." | |
| Unlikely bomber | Unlikely bomber |
| Hard to imagine a five-year-old or a 90-year-old becoming radicalised. | Hard to imagine a five-year-old or a 90-year-old becoming radicalised. |
| But if people like that were never checked, a terrorist could see an opportunity. | But if people like that were never checked, a terrorist could see an opportunity. |
| Umar Farouk Abdulmutallab is accused of trying to bomb an airliner | Umar Farouk Abdulmutallab is accused of trying to bomb an airliner |
| There is a famous example of an apparently unlikely bomber - a young pregnant Irish woman called Anne-Marie Murphy, who was planning to fly from London to Israel in 1986, recounts Philip Baum, editor of Aviation Security International. | There is a famous example of an apparently unlikely bomber - a young pregnant Irish woman called Anne-Marie Murphy, who was planning to fly from London to Israel in 1986, recounts Philip Baum, editor of Aviation Security International. |
| Ms Murphy's boyfriend - who, unknown to her, was a Jordanian militant - had planted explosives on her, hoping she would get on to the flight without arousing suspicion, Baum says. | Ms Murphy's boyfriend - who, unknown to her, was a Jordanian militant - had planted explosives on her, hoping she would get on to the flight without arousing suspicion, Baum says. |
| But in this instance, Baum notes, the plot was stopped because of the intense passenger profiling carried out by Israeli flight security. Ms Murphy did not seem like a typical traveller for that flight. | But in this instance, Baum notes, the plot was stopped because of the intense passenger profiling carried out by Israeli flight security. Ms Murphy did not seem like a typical traveller for that flight. |
| To make sure innocent people are not used in this way, passengers should be selected for extra checks using a graded scale of risk, according to Prof Spieglhalter. | To make sure innocent people are not used in this way, passengers should be selected for extra checks using a graded scale of risk, according to Prof Spieglhalter. |
| A computer scientist from the University of Texas, William Press, believes he has done the maths to come up with a good way of doing exactly that. | A computer scientist from the University of Texas, William Press, believes he has done the maths to come up with a good way of doing exactly that. |
| Additional checks | Additional checks |
| Suppose you have two people - passenger X and passenger Y - and your brilliant profiling suggests Mr X is 100 times more likely than Mr Y to be a terrorist. | Suppose you have two people - passenger X and passenger Y - and your brilliant profiling suggests Mr X is 100 times more likely than Mr Y to be a terrorist. |
| Your stats tell you to pick out Mr X for additional security checks 100 times more often than Mr Y. | Your stats tell you to pick out Mr X for additional security checks 100 times more often than Mr Y. |
| But William Press says that would be a mistake. | But William Press says that would be a mistake. |
| Security resources are finite, and the threat is varied | Security resources are finite, and the threat is varied |
| He says if you take the square root of their risk it narrows the gap between them - so you check Mr X only 10 times more often than Mr Y. | He says if you take the square root of their risk it narrows the gap between them - so you check Mr X only 10 times more often than Mr Y. |
| That means you do not expend all your resources checking only one tiny group of people every time they turn up at an airport - and hardly ever checking people who pose a lower risk, but still a risk. | That means you do not expend all your resources checking only one tiny group of people every time they turn up at an airport - and hardly ever checking people who pose a lower risk, but still a risk. |
| Basically, you widen your net. | Basically, you widen your net. |
| In reality, of course, your intelligence is unlikely to be as brilliant as that example suggests. | In reality, of course, your intelligence is unlikely to be as brilliant as that example suggests. |
| Getting good and useful data for profiling is difficult. | Getting good and useful data for profiling is difficult. |
| But, even if you supposed you had an almost perfectly accurate profiling system, there is another problem - terrorists are very rare and that leads to some counter-intuitive statistics. | But, even if you supposed you had an almost perfectly accurate profiling system, there is another problem - terrorists are very rare and that leads to some counter-intuitive statistics. |
| If someone is stopped by security for extra checks because they seem to pose a potential risk, they are almost certainly innocent, Prof Spiegelhalter suggests. | If someone is stopped by security for extra checks because they seem to pose a potential risk, they are almost certainly innocent, Prof Spiegelhalter suggests. |
| "There are more than a 100 million people flying out of UK airports every year and you might be trying to foil one or two terrorist plots," he says. | "There are more than a 100 million people flying out of UK airports every year and you might be trying to foil one or two terrorist plots," he says. |
| "Even if you had a profiling system that was 99.99% accurate, there would be 1 in 10,000 errors. | "Even if you had a profiling system that was 99.99% accurate, there would be 1 in 10,000 errors. |
| "If you consider that around 100 million people go through UK airports each year, that would mean 10,000 innocent people would trigger the system." | "If you consider that around 100 million people go through UK airports each year, that would mean 10,000 innocent people would trigger the system." |
| "I would hope that in any training of staff, this is really rammed home. | "I would hope that in any training of staff, this is really rammed home. |
| "If you're not going to cause enormous resentment about this, it's got to be very delicately handled - maths tells you that." | "If you're not going to cause enormous resentment about this, it's got to be very delicately handled - maths tells you that." |
| So although statistics could help catch terrorists, to some degree, they do not make it easy, and they probably will not get you through airport security any quicker. | So although statistics could help catch terrorists, to some degree, they do not make it easy, and they probably will not get you through airport security any quicker. |