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Homework Help: Probability of disease

  1. Jun 12, 2007 #1
    1. The problem statement, all variables and given/known data

    Approx. 1/1000 has a disease, and the method of testing has a 5 % false positive rate. If a random person tests positive, what is the probability that he has the disease?

    2. Relevant equations

    I'm pretty sure Baye's theorem is the thing to use.

    3. The attempt at a solution

    I'm having trouble defining my probabilities. I've defined that P(sick) = 0,001 and P(not sick|+) = 0,05. But then I'm stuck...
     
  2. jcsd
  3. Jun 12, 2007 #2

    NateTG

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    You could try the problem this way:

    Let's say we test 1,000 people:
    How many false positives do we expect to get?
    How many real positives do we expect to get?
     
  4. Jun 12, 2007 #3
    Well, wouldn't that be 50 and 1?
     
  5. Jun 13, 2007 #4

    NateTG

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    So, how likely is a positive test to indicate disease?
     
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