Thus out of every 100 people who do not have the A80 mutation 10 tested

# Thus out of every 100 people who do not have the a80

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Thus, out of every 100 people who do not have the A80 mutation, 10 tested positive (false positives) and 90 were true negatives (100 - 10). Thus the test has a specificity of 90%. Method 2 for figuring out the true negative rate: You could also use the formula you learned in Biostats: TNR = TN/N = TN / (TN + FP) = 450 / (450 + 50) = 450/500 = 0.9 = 90/100 = 90% Where TNR = true negative rate = people without disease who test negative N = all tested people who do not have the disease TN = true negatives = people without disease who test negative FP = people without disease who test positive A follow up study of the false positives in the first study revealed that some had a slightly different mutation (mutation A81) that is in the same gene but does not lead to disease. A study comparing the new rapid test to the older, definitive test is conducted on people who have either the A80 or the A81 mutation, and yields the following data:

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Jaisri Lingappa, MD PhD Science in Public Health, SPH381 2 Using the rapid test: Out of 500 people who have either the A80 or A81 mutation, 410 tested positive. Out of 500 people who do not have either the A80 or A81 mutation, nobody tested positive. Question 3: What is the sensitivity of the rapid test for detecting the A80 or A81 mutation? Sensitivity is the true positive rate. Here that means the number of people with the A80 or A81 mutation who test positive. To figure out the rate, first convert to 100 people total, which in this case means dividing all numbers by 5. This shows you that for every 100 people who have the A80 or A81 mutation, 82 tested positive. Thus, the test has a sensitivity of 82%. Or if you use the formula: TPR = TP/P = TP/ (TP +FN) =410/(410 + 90) = 410/500 = 0.82 = 82/100 = 82% sensitivity Question 4: What is the specificity of this test for detecting the A80 or A81 mutation? Specificity is the true negative rate. Here that means the number of people the A80 or A81 mutation who test negative. Once again you were given the number of false positives, which is the inverse of the number of true negatives. Since no one had a false positive, 100% of actual negatives had negative tests. Thus, the test has a specificity of 100%. Or if you use the formula: TNR = TN/N = TN / (TN + FP) = 500 / (500 + 0) = 500/500 = 1.0 = 100/100 = 100 % specificity Question 5: The rapid test is less expensive than the definitive test for the A80 mutation. Given this, propose a strategy for using these two tests in combination that would be a cost-effective and accurate screen to identify people who have the A80 mutation (who will get the disease) but not the A81 mutation (which does NOT cause disease). Will anyone with disease be missed with your strategy, and if so, why?
• Spring '19
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