Tuesday, February 27, 2007

Probable Cause

Britneys hair, abortion, police checks where is your probable cause?
You guys got nothing on me. Where's your probable cause?
You're a known hijacker. You're sweating like a guilty motherfucker. That's my p.c. Save us the time. Tell us where the truck is.
Fenster knocks on the table.
HELLO? Can you hear me in the back? P.C.
He looks under his chair.
Where is it? I'm lookin'. It's not happening. What's going on with that?

Before testing for something you need a reasonable expectation a reasonable suspicion that it is true. That is why we have search warrants and why rare diseases should only be tested for if there is a family history of them. If you test everyone for something that is rare even with a very accurate test you end up mainly with false positives

Say 1% of people have something nasty you want to test for. Say the test is 99% correct if it says you are on drugs. That means that the test is actually 50:50. 2 people in a hundred will be found to be on drugs, only one will be.

For nasty things that are rarer such as inherited diseases or being a terrorist the innocent:guilty ratio based on an “accurate” test is even worse.

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