Question 3 Out of 1000 people without HIV infection how many will have false

# Question 3 out of 1000 people without hiv infection

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Question 3: Out of 1000 people without HIV infection, how many will have false positive results with test 1? Specificity is the true negative rate, meaning the number of people without disease who test negative. Specificity is also the inverse of the false positive rate. Thus, a test with an 80% specificity has a 20% false positive rate. Thus, 200 out of 1000 people without HIV infection will test positive with test 1. Question 4: Out of 1000 people without HIV infection, how many will have false positive results with test 2? Specificity is the true negative rate, meaning the number of people without disease who test negative. Specificity is also the inverse of the false positive rate. Thus, a test with 99.9% specificity has a 0.1% false positive rate (100% - 99.9% = 0.1%). Thus, 1 out of 1000 people without HIV infection will test positive with test 2. For people who are being tested for the first time after becoming HIV positive, what are the advantages and disadvantages of the two tests? Which test should the clinic choose as a screening test for its patients? The advantage of test 1, which has a high sensitivity, is that it will identify nearly all people with HIV infection; however, the disadvantage is that it will also result in a false positive test for 20% of people who are not HIV infected. To use this test, one would need to implement a follow up test in which all people who test positive undergo a second test with high specificity before receiving a diagnosis. The advantage of test 2, which has high specificity, is that it has a very low false positive rate and therefore will only rarely yield a positive test in a person without HIV infection. However, the disadvantage is that 15 out of 1000 people with HIV disease will be missed using this test due to its low sensitivity. Since the number of people who will test positive is smaller than the number of people who will likely test negative, it is much easier to do a second screening test on people with a positive test than on people with a negative test. Thus, test 1 will most likely be easier to implement as a first screen. Note that test 2 could function as a secondary test, given its very high specificity.
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