The results of a study investigating a new diagnostic test for acute myocardial infarction (MI) are given in the table below. What is the sensitivity of the new diagnostic test?

Question

The results of a study investigating a new diagnostic test for acute myocardial infarction (MI) are given in the table below.  What is the sensitivity of the new diagnostic test?

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11ec160b_3723_d85c_9249_3d80bb8f6a1b_MD0001_00 The data is presented in the standard 2 × 2 (contingency) table format. The sensitivity of a test refers to its ability to correctly identify individuals affected with a disease. It is the number of true positives divided by the total number of patients with the disease. Sensitivity should be high in screening tests in order to pick up all cases of a disease (decrease false negatives). Using the generic 2 × 2 (contingency) table: Sensitivity = TP / (TP + FN), where TP is true positives and FN is false negatives. In this case: (Choice A) The false negative rate is (1 - sensitivity) = 1 - 0.75 = 0.25 (or 25%). The false negative rate is not affected by disease prevalence. (Choice B) The value 37.5% is obtained by dividing the TP (75) by the total number of patients in the study (75 + 25 + 20 + 80 = 200). (Choice C) The number of patients with myocardial infarction (MI) based on the gold standard is 100 (= 75 + 25). The total number of patients in the study is 200 (= 75 + 25 + 20 + 80). Therefore, the prevalence of MI in this sample is 100/200 = 0.5 (or 50%). (Choice E) The positive predictive value (PPV) of the test (the probability that a person has the disease given a positive test result) is given by: PPV = TP / (TP + FP), where FP is false positives. In this case, PPV = 75 / (75 + 20) = 75/95 = 0.79 (or 79%). (Choice F) The test specificity (its ability to correctly identify individuals without the disease) is 80 / (80 + 20) = 80/100 = 0.80 (or 80%). Educational objective: Sensitivity = true positives / (true positives + false negatives). Screening tests should have high sensitivity.

The Results of a Study Investigating a New Diagnostic Test