## Quiz 6: First B Level Question |
AZobi |
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A certain disease has a prevalence of one percent in a population. A test, Test A, has a false positive rate of .2 and a false negative rate of .01. This test is a screening test. Test B has a false positive rate of .02 and a false negative rate of .15. This test is a conﬁrmatory test. The false positive and false negative rates of the tests depend only on whether or not a person has the disease. Test B is only given to a patient if the patient tests positive on Test A. What is the probability that a person who tests positive on Test B has the disease? |

AZobi: March 4, 2015, 2:26 a.m. |
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Not sure about this, but my answer is: [(.05)(.05)(.99)+(.92)(.92)(.01)]/[(.92)(.92)(.01)+(.08)(.92)(.01)+(.05)(.05)(.99)+(.95)(.05)(.99)] |

dynguyen: March 5, 2015, 1:19 a.m. |
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Hi there, not too sure about my answer either. Since we're looking for P(D|+B), we have to find P(D n +B) and divide it by P(+B). I got [(.01)(.99)(.85)] / [(.01)(.99)(.85) + (.99)(.2)(.02)] |

dynguyen: March 5, 2015, 1:32 a.m. |
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I think you switched your answers for B and A! |

AZobi: March 5, 2015, 2:15 a.m. |
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You are right! So sorry about that. |

AZobi: March 5, 2015, 2:16 a.m. |
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My answer: [(.85)(.99)(.01)]/[(.85)(.99)(.01)+(.02)(.2)(.99)]. |

martha2A: March 5, 2015, 8:12 p.m. |
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Yup! I got that too :) |

AZobi: March 5, 2015, 8:28 p.m. |
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Yay! :) |

weisbart: March 8, 2015, 1:03 p.m. |
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Awesome guys! |