Tests for tuberculosis like all other diagnostic tests are not perfect. QFT-G is one of such tests for tuberculosis. Suppose that for the population of adults that is taking the test, 5% have tuberculosis. The test correctly identifies 74.6% of the time adults with a tuberculosis and correctly identifies those without tuberculosis 76.53% of the time. Suppose that POS stands for the test gives a positive result and S means that the adult really has tuberculosis. What is the probability of an adult getting a NEG result and truly having tuberculosis?

Question

Rosemary Conley

Mathematics

25 November, 16:27

Tests for tuberculosis like all other diagnostic tests are not perfect. QFT-G is one of such tests for tuberculosis. Suppose that for the population of adults that is taking the test, 5% have tuberculosis. The test correctly identifies 74.6% of the time adults with a tuberculosis and correctly identifies those without tuberculosis 76.53% of the time. Suppose that POS stands for the test gives a positive result and S means that the adult really has tuberculosis. What is the probability of an adult getting a NEG result and truly having tuberculosis?

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Travis Lowe · Answer 1

the probability of an adult getting a NEG result and truly having tuberculosis is 0.0127

Step-by-step explanation:

S = the adult really has tuberculosis.

S' = complement of S = the adult does not has tuberculosis.

POS = the test gives a positive result

P (S) = 0.05

P (POS | S) = 0.746

P (NEG | S') = 0.7653

this is an intersection because the "and" word

P (NEG ∩ S) = P (NEG| S) * P (S) = (1-P (POS | S)) * P (S) = (1-0.746) * 0.05=0.0127