Bayes theorem pops up in another unlikely place
… or why data mining is a good way to find stolen credit cards and not at all a good way to find terrorists:
No matter how sophisticated and super-duper are NSA’s methods for
identifying terrorists, no matter how big and fast are NSA’s computers,
NSA’s accuracy rate will never be 100% and their misidentification rate
will never be 0%. That fact, plus the extremely low base-rate for
terrorists, means it is logically impossible for mass surveillance to
be an effective way to find terrorists.
– via Bruce Schneier, who knows a thing or two about this stuff.