John Cochrane wrote on 4/17/2020 8:22 PM:

A test that is wrong 50% of the time can be replaced with a coin toss.


Not true actually, a test with a 50% chance of being wrong can be quite useful.

Suppose 2% of the population has the disease. Take a test that has 100% chance of positive if you do have it, and 50% chance of positive if you don't have it. It tells the 2 people who do have it they have it, and it tells one other healthy person he has it too. Three people stay home, 97 go soaring in perfect safety.

Take a test that has 100% chance of negative if you don't have it, but 50% chance of positive if you do have it. 98 people are correctly cleared, 1 person is incorrectly cleared, 1 stays home. Well, we got half the sick people out of the population and reduced the reproduction rate by half.

John Cochrane.

Bob's description of the test seem to indicate it was wrong 50% of the time for
positive people, and wrong 50% of the time for negative people, so your results
would always be 50% positive, regardless of the actual percentage of positive people.

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Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
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