How is the specificity of a screening test calculated?
A) True positives/Total diseased
B) True negatives/Total not diseased
C) False negatives/Total diseased or 1 – Sensitivity
D) False positives/Total not diseased or 1 – Specificity
Ans: B
Specificity (true-negative rate) is calculated as True negatives/Total not diseased. Sensitivity (true-positive rate) is calculated as True positives/Total diseased. False-negative rate is calculated as False negatives/Total diseased or 1 – Sensitivity. False-positive rate is calculated as False positives/Total not diseased or 1 – Specificity.
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