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Math Help - stats

  1. #1
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    Mar 2008
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    stats

    i am looking for some help with this question,

    a drug test is 88% effective in detecting drugs when it is present, it also yeilds a false positive result for clean people 3% of the time. If 1 percent are drug users what is the probability that a person testing positive actually used the drug?

    thanks
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  2. #2
    Member
    Joined
    Mar 2008
    Posts
    148
    I am thinking 88% of 1% plus 3% of 99% will test positive for the drug.

    The idea being that 1% of people actually use drugs and 88% of the time these people will test positive, while 99% of people do not use drugs and 3% of the time they will test positive.

    .88*.01 + .03*.99 = .0385

    .01 is 25.97% of .0385

    So there is a 25.97% chance that a person testing positive actually did take the drug. What do you think?
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