A 99% accurate medical test can be wrong half of the time.

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O4L

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I know it sounds like a Yogi Berra quote but it is actually true.

https://www.concordmonitor.com/medical-tests-positive-statistics-27349847

Imagine a town of 10,000 people in which 1% of the population has a deadly disease. You want to find out who those people are using a test that’s 99% accurate, so you give the test to everybody.

There are 100 people in town who have the disease – that’s 1% of the total population – and the test finds 99 of them, missing just a single sick person. Well done!

But remember that 9,900 of the people who were tested do not have the disease. The test is 99% accurate so it knows that 9,801 of them are healthy. What a relief!

But since the test is sometimes wrong, it incorrectly says that 1% of the healthy people are infected. That’s 99 people, all of whose lives are turned upside down when they’re told (incorrectly) that they have a deadly disease.

Look at those results again. Testing the whole population for a rare disease produced 198 positive results, but one-half of them were wrong: 99 of the people were sick but 99 were actually healthy.

A 99% accurate result was wrong half the time. Truly that’s a Paradox from Prediction of Positive results. Triple P in action!
 

RickN

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"How can a medical test that is 99% accurate be wrong half the time, even when it is performed correctly?The answer: When the disease is rare."
 

O4L

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"How can a medical test that is 99% accurate be wrong half the time, even when it is performed correctly?The answer: When the disease is rare."
Yep. Kind of like the covid rate in the US.

( BTW which is based on high false positive testing.)
 

O4L

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"The situation is worse in real life because no medical test is that accurate. Even 95% accuracy is excellent, yet in the above scenario a 95% test would produce 495 false positives – people told incorrectly that they had a deadly disease – for just 95 correct positives, an error rate of 4-to-1."
 

Uncle TK

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A person drive 60 miles at 30 Miles per hour.
On the return trip he wants to average 60 Miles per hour.
How fast must he drive on the return trip to average 60 miles per hour.
(Answer is it is impossible) this is basic Statistics
 

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