TIA and CAPPS:  The Math

I’ve seen a couple of articles on this concept.  The basic story is that, due to the relatively large number of innocent versus guilty people, anything other than a 100% correct database (checked your credit report lately?) will wrongly punish a much larger number of innocent people than wrongly allow guilty ones to go free.

Example 3: Assume a 1% error rate — one in a hundred — and the same one in 10,000 ratio of guilty people. The results are very different. For every 100 guilty people the database correctly identifies, it will mistakenly identify 10,000 innocent people as guilty. The number of guilty people erroneously listed as innocent is larger, but still very small: one in 100.

Another interesting tidbit:

There are 13 million people on the FBI’s terrorist watch list. That’s ridiculous, it’s simply inconceivable that a number of people equal to 4.5% of the population of the United States are terrorists. … And in any case, any watch list with 13 million people is basically useless. How many resources can anyone afford to spend watching about one-twentieth of the population, anyway?

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