[muget]

Suppose that a medical test for a particular disease has a very high success rate: if a tested patient has the disease, the test accurately reports this, a'positive',99% of the time, and if a tested patient does not have the disease, the test accurately reports that, a'negative',95% of the time. Suppose also,however, that only 0.1% of the population have that disease. (a) Compute the probability of a false positive given the test was positive.(b)for the medical test described above, what is the probability that a person chosen at random will get a negative report in the test.

[ebaines]

I'll help to get you started. An easy way to think through this is to consider a population of 1 miilion people taking the test. Of this group we expect 0.1% to have the disease, or 1000 people. Which means 999,000 people do not have the disease. Of the 1000 who have it, the test will give 99% x 1000 = 990 corrrect positives and 10 incorrect negatives. Of the people who do not have the disease the test gives 95% x 999,000 = 949,050 correct negatives, and 5% or 49,940 incorrect negatives. You now have enough data to answer the two questions. You should find that the proibabiliy of a positive result being false is quite high. Post back and tell us what you get for answers.