What are the odds ...?
From the latest BBC Magazine
...Imagine you've invented a machine to detect terrorists. It's good, about 90% accurate. You sit back with pride and think of the terrorists trembling.
You're in the Houses of Parliament demonstrating the device to MPs when you receive urgent information from MI5 that a potential attacker is in the building. Security teams seal every exit and all 3,000 people inside are rounded up to be tested.
The first 30 pass. Then, dramatically, a man in a mac fails. Police pounce, guns point.
How sure are
you that this person is a terrorist?
A. 90%
B. 10%
C. 0.3%
PC World is New Zealand’s top selling computing and technology magazine.
Comments
Nice! Once thing I don't get how BBC editor couldn't do a division and made an error. Oh boy :-(
Posted by: macias | July 29, 2009 8:56 AM
Ah.. a classic. A test designed to detect something very very rare has to do a lot better that 90% accuracy.
Posted by: manu | July 29, 2009 2:45 AM