Screening test sensitivity, specificity, and predictive value concepts applied to public health screening program decisions.
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- What is sensitivity in a screening test?
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The proportion of people who truly have the disease who test positive (true positive rate).- What is specificity in a screening test?
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The proportion of people who truly do not have the disease who test negative (true negative rate).- What is the formula for sensitivity?
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TP / (TP + FN)- What is the formula for specificity?
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TN / (TN + FP)- What is positive predictive value (PPV)?
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The proportion of people with a positive test result who actually have the disease.- What is negative predictive value (NPV)?
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The proportion of people with a negative test result who actually do not have the disease.- What is the formula for positive predictive value?
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TP / (TP + FP)- What is the formula for negative predictive value?
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TN / (TN + FN)- How does increasing disease prevalence affect PPV, for a test with fixed sensitivity and specificity?
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PPV increases as prevalence increases.- How does increasing disease prevalence affect NPV, for a test with fixed sensitivity and specificity?
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NPV decreases as prevalence increases.- Does a test's sensitivity change with disease prevalence in the population tested?
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No, sensitivity is an intrinsic property of the test and does not depend on prevalence.- Does a test's specificity change with disease prevalence in the population tested?
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No, specificity is an intrinsic property of the test and does not depend on prevalence.- What is a highly sensitive test useful for when its result is negative?
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Ruling out disease.- What is a highly specific test useful for when its result is positive?
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Ruling in disease.- What test characteristic is prioritized for an initial population screening test?
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High sensitivity, so as few true cases as possible are missed.
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