Beach Day by Rodger Bliss
September 2022
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False Positive

You are tested for a rare flesh-eating virus that afflicts 1% of the population. If you have the virus, the test will always come back positive, but if you do not, there is a 20% chance of a false positive. You are told that your test came back positive. What is the probability that you have the disease?

 

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4 guesses to False Positive


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  • Dude

    No, keep guessing.

  • Dude

    5% is correct, Eliza Beth.

    n=100 was used and numbers are rounded to whole people.

    Of 100 people, 1 true positive and 20 false positive results are reported.

    A total of 21 positives are reported and thus, 1/21 positives are true positives.

    1/21 x 100% = 5%

    That is the answer, of the 21 positive results, he has a 5% chance of being one of the fortunate 20.

    Great job! You’re today’s winner.