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?
- The proportion of people who truly have the disease who test positive (true positive rate).
- What is specificity in a screening test?
- The proportion of people who truly do not have the disease who test negative (true negative rate).
- What is the formula for sensitivity?
- TP / (TP + FN)
- What is the formula for specificity?
- TN / (TN + FP)
- What is positive predictive value (PPV)?
- The proportion of people with a positive test result who actually have the disease.
- What is negative predictive value (NPV)?
- The proportion of people with a negative test result who actually do not have the disease.
- What is the formula for positive predictive value?
- TP / (TP + FP)
- What is the formula for negative predictive value?
- TN / (TN + FN)
- How does increasing disease prevalence affect PPV, for a test with fixed sensitivity and specificity?
- PPV increases as prevalence increases.
- How does increasing disease prevalence affect NPV, for a test with fixed sensitivity and specificity?
- NPV decreases as prevalence increases.
- Does a test's sensitivity change with disease prevalence in the population tested?
- 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?
- 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?
- Ruling out disease.
- What is a highly specific test useful for when its result is positive?
- Ruling in disease.
- What test characteristic is prioritized for an initial population screening test?
- High sensitivity, so as few true cases as possible are missed.