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  1. #1
    Super Moderator BATcher's Avatar
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    Health screening

    Imagine there is a condition in the population that affects one in 1000 people.

    A test is developed which is 95% accurate - it gives false positives in 5% of cases and it doesn't give any false negatives.
    You take the test and it tells you that you have the condition.

    How likely is it that you actually do have the illness, and why did you choose that answer?

    a) 95%

    100%

    c) 2%
    BATcher

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  2. #2
    Plutonium Lounger
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    Re: Health screening

    <span style="background-color: #FFFF00; color: #FFFF00; font-weight: bold">2%
    If 1000 people are tested then one will have the disease and 5% of them (50) will receive a false positive. This means that out of every 51 positive results only 1 person has the disease, so you have one chance in 51 of having the disease. This is slightly below 2%.</span hide>

    StuartR

  3. #3
    Super Moderator BATcher's Avatar
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    Re: Health screening

    Yes, entirely correct!

    There are a few other puzzles in the location from where I filched the first one...
    BATcher

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  4. #4
    Plutonium Lounger
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    Re: Health screening

    Nice puzzles, but I disagreed with the answer to the first one!

    StuartR

  5. #5
    Super Moderator BATcher's Avatar
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    Re: Health screening

    And in the puzzle about the boat carrying a wolf, a goat and some cabbages, the suggestion was that the answer could be just ONE trip -
    <UL><LI>if you put the wolf first into the boat, <LI>then strapped the goat to its back, so the wolf could not reach the goat,<LI>then strapped the cabbages to the back of the goat, so the goat could not reach them![/list]"Good luck with this!" I say...
    BATcher

    Time prevents everything happening all at once...

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