For the sake of argument, let us say one out of every million people is a terrorist (an overestimate). Let us also imagine there exists a machine that can determine whether someone is a terrorist with 99.9 percent accuracy.
What are the odds an individual tested is a terrorist? 0.1 percent chance right?
So the 99.9 percent accurate test will give you the wrong answer 99.9 percent of the time. Seem low? This is what is known as the false positive paradox, and it completely dismantles any possible justification for the NSA’s dragnet surveillance of our phone calls and emails.
The argument was first put forward by Cory Doctorow in his book Little Brother.
“When you try to find something really rare, your test’s accuracy has to match the rarity of the thing you’re looking for,” Doctorow says. “If it does not, then the number of false positives will completely bury the signal in irrelevant garbage.”
The numbers used beforehand are generous. The NSA procedure for identifying terror suspects is almost certainly less than 99.9 percent accurate. Instead, it’s a compete snow job that has yet to produce any significant success…
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