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Unformatted text preview: topic covered in this chapter is another frequently misunderstood aspect of probability. This is the so called confusion of the inverse. Consider the following situation (this is Thought Question 3 on page 335): A certain disease affects 1 in every 1000 people. A test for this disease has a false positive rate of 10% and a false negative rate of 10%. This means that the test is about 90% accurate. Question: If you test positive for the disease, what is the probability that you actually have the disease? Let’s begin with some definitions: 1. A medical test is a procedure for finding the presence of a disease or a condition, usually when the disease is not directly observable. It is often indirect. Thus a test for bacterial infection may use a white cell blood count. 2. The sensitivity of a test is a measure of the test’s ability to detect the presence of a disease. If a test for bacterial infection is 97% sensitive, it means that out of 100 cases of bacterial infection, it will produce a positive test result in 97 of those cases. It will miss 3 of the cases. These are...
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 Fall '13

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