Predictive value depends on which factors for a diagnostic test?

Predictive value depends on which factors for a diagnostic test?

• A. Only test sensitivity
• B. Only prevalence
• C. Both disease prevalence and test sensitivity/specificity
• D. None

Answer: (C)

Predictive value tells you how likely a test result reflects the true disease status. Whether a positive result really means disease (positive predictive value) or a negative result truly means no disease (negative predictive value) depends on two things: how common the disease is in the group being tested (prevalence) and how good the test is at detecting disease (sensitivity) and ruling it out (specificity). If the disease is rare, a positive result is more likely to be a false alarm, which lowers the predictive value of a positive test even if sensitivity and specificity are high. If the disease is common, a positive result is more likely to be a true positive, raising predictive value. The same reasoning applies to negative results and the negative predictive value. So, predictive value hinges on both prevalence and the test’s performance characteristics, not on prevalence alone or on sensitivity/specificity alone.

Predictive value tells you how likely a test result reflects the true disease status. Whether a positive result really means disease (positive predictive value) or a negative result truly means no disease (negative predictive value) depends on two things: how common the disease is in the group being tested (prevalence) and how good the test is at detecting disease (sensitivity) and ruling it out (specificity).

If the disease is rare, a positive result is more likely to be a false alarm, which lowers the predictive value of a positive test even if sensitivity and specificity are high. If the disease is common, a positive result is more likely to be a true positive, raising predictive value. The same reasoning applies to negative results and the negative predictive value. So, predictive value hinges on both prevalence and the test’s performance characteristics, not on prevalence alone or on sensitivity/specificity alone.