A study was undertaken to evaluate the use of computed tomography (CT) in the diagnosis of lumbar disk herniation. Eighty patients with lumbar disk herniation confirmed by surgery were evaluated with CT, as were 50 patients without herniation. The CT results were positive in 56 of the patients with herniation and in 10 of the patients without herniation. The sensitivity of CT for lumbar disk herniation in this study is
The correct answer is C.
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"Sensitivity" is best defined as:
The correct answer is A. You answered D.
The correct answer is "A." Sensitivity refers to how often the test will pick up the disease if it is there. The equation is: Sensitivity = true positives/(true positives + false negatives). Note that the sum of true positives + false negatives represents all of the people with disease.
You have invented a blood test, which you name “veritangin,” to determine if patients are having a myocardial infarction. You devise an experiment to determine the performance of your veritangin assay by testing it versus the troponin assay, the currently accepted gold standard for determining myocardial infarction, in 100 random emergency department patients with chest pain. You choose a veritangin result >1 ng/dL as positive for myocardial infarction. Your results are listed in the table below.
| Troponin Status | ||
|---|---|---|
| Veritangin Status | Troponin Positive | Troponin Negative |
| Veritangin Positive | 15 | 5 |
| Veritangin Negative | 10 | 70 |
Which of the following statements regarding the characteristics of the veritangin assay in this trial is true?
A receiver operating characteristic (ROC) curve is constructed for a new test developed to diagnose disease X. All of the following statements regarding the ROC curve are true EXCEPT:
One criticism of the ROC curve is that it is developed for testing only one test or clinical parameter with exclusion of other potentially relevant data.
ROC curve allows the selection of a threshold value for a test that yields the best sensitivity with the fewest false-positive tests.
The axes of the ROC curve are sensitivity versus 1 – specificity.
The ideal ROC curve will have a value of 0.5.
The value of the ROC curve is calculated as the area under the curve generated from the true-positive rate versus the false-positive rate.
The answer is D. A receiver operating characteristic (ROC) curve plots sensitivity (or true-positive rate) on the y-axis and 1 – specificity (or false-positive rate) on the x-axis. Each point on the curve represents a cutoff point of sensitivity and 1 – specificity, and these cutoff points are used to select the threshold value for a diagnostic test that yields the best trade-off between true-positive and false-positive tests. The area under the curve can be used as a quantitative measure of the information content of a test. Values range from 0.5 (a 45 degree line), representing no diagnostic information, to 1.0 for an ideal test. In the medical literature, ROC curves are often used to compare alternative diagnostic tests, but the interpretation of a specific test and ROC curve is not as simple in clinical practice. One criticism of the ROC curve is that it evaluates only one test parameter with exclusion of other potentially relevant clinical data. Also, one must consider the underlying population in which the ROC curve was validated and how generalizable this is to the entire population with disease.
Reference: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1065080/