A fascinating and easy to follow

It tells a story of going to a doctor because you feel ill, and the doctor thinks you might have a quite rare disease which affects 0.1% of the population.

So the doctor orders a blood test that can accurately detect this disease with 99% sensitivity (meaning the test correctly detects the presence of this disease in 99% of cases, and only produces a false positive result in 1% of cases).

The results of your test come back, and the test finds you positive.

So given this positive test result, what are the chances that you actually have the disease?

Most people would probably say that there is a 99% chance they have the disease.

But in fact that's completely wrong! The video explains that because of Bayes law, the chances of you having this disease given the positive test result are only 9%!

See the

**short video**explains Bayes law, as applied to medical tests.It tells a story of going to a doctor because you feel ill, and the doctor thinks you might have a quite rare disease which affects 0.1% of the population.

So the doctor orders a blood test that can accurately detect this disease with 99% sensitivity (meaning the test correctly detects the presence of this disease in 99% of cases, and only produces a false positive result in 1% of cases).

The results of your test come back, and the test finds you positive.

So given this positive test result, what are the chances that you actually have the disease?

Most people would probably say that there is a 99% chance they have the disease.

But in fact that's completely wrong! The video explains that because of Bayes law, the chances of you having this disease given the positive test result are only 9%!

See the

**video at 2:06**for an easy to understand explanation.
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