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A common misunderstanding.


I read something amazing the other day and I am sure I had read it before but you know how these things slip sometimes… anyway…

Imagine there is a test for a disease or condition that someone conducts on you. Here I am imagining a doctor performing a blood test for a serious diesease, but any scenario still holds.

The test is conducted on you and lo and behold to your horror, it is positive. Worse still, the doctor informs you sadly that the test is 99% accurate.

So do you have the disease or not? What are your chances of not having the disease?

Explanation coming soon but to not leave anyone in suspense, it is not 99% certain you have the disease, oh no, not at all, not by a very long way. In fact in certain situations you are still more likely not to have the disease than to have it. Even if the test is 99.99% accurate.

Anyone care to guess why?

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