Monday, 28 December 2009

Calculated risks

Nate Silver over at FiveThirtyEight runs the kind of back-of-the-envelope calculation on the risks of being in a hijacked aircraft that you might expect as part of a McKinsey interview.
There were a total of 674 passengers, not counting crew or the terrorists themselves, on the flights on which these incidents occurred. By contrast, there have been 7,015,630,000 passenger enplanements over the past decade. Therefore, the odds of being on given departure which is the subject of a terrorist incident have been 1 in 10,408,947 over the past decade. By contrast, the odds of being struck by lightning in a given year are about 1 in 500,000. This means that you could board 20 flights per year and still be less likely to be the subject of an attempted terrorist attack than to be struck by lightning.
What's the most you'd pay for insurance against a 1 in 10.4 million event? Since the value of a statistical life, backed out of these kinds of calculations, is $7 million, our best guess is that folks would be unwilling to spend more than a dollar to insure against this risk. I get the feeling that the TSA's budget is considerably more than that.

Ok, class: Assume that if you reduce TSA spending by an order of magnitude the risk of a terrorist incident also rises by an order of magnitude. By how many orders of magnitude ought the TSA budget be reduced to get spending to a level commensurate with the estimated risks?