A diagnostic test for a rare genetic disorder correctly identifies 90% of individuals without the condition. Out of 50 individuals tested negative for the disorder, 5 are falsely classified as negative. Which of the following is the negative predictive value for this test?
E) 90%
Negative predictive value (NPV) is the probability that a negative test result truly indicates the absence of the disease. It is calculated as true negatives/(true negatives + false negatives). In this case, NPV = 45/(45 + 5) = 45/50 = 0.90 or 90%.
Answer choice A: 10%, is incorrect. This value represents the sensitivity of the test, which is the probability of a negative test result when the disease is absent.
Answer choice B: 45%, is incorrect. This value is not the correct calculation for the given scenario.
Answer choice C: 50%, is incorrect. This value is not the correct calculation for the given scenario.
Answer choice D: 89%, is incorrect. This value is not the correct calculation for the given scenario.
Key Learning Point
Negative predictive value is the probability that a negative test result truly indicates the absence of the disease. It is calculated as true negatives/(true negatives + false negatives). NPV is a critical measure for understanding the reliability of a negative test result in excluding a particular condition in a given population.
