What is the positive predictive value (PPV) in diagnostic testing?

What is the positive predictive value (PPV) in diagnostic testing?

• A. Probability that a positive test result indicates the presence of disease
• B. Probability that a negative test result indicates absence of disease
• C. Proportion of the population that has the disease
• D. Incidence rate of disease in the population

Answer: (A)

The positive predictive value is the probability that a positive test result actually indicates the presence of disease. In practical terms, it answers: if the test comes back positive, how likely is it that the person truly has the disease? PPV is calculated as true positives divided by all positive test results (PPV = TP / [TP + FP]). This value depends not only on the test’s accuracy (sensitivity and specificity) but also on how common the disease is in the population (prevalence). When the disease is rare, many positives can be false positives, lowering the PPV; when the disease is common, the PPV increases. Why the other ideas don’t fit: the probability that a negative result means the disease is absent is the negative predictive value; the proportion of the population that has the disease is prevalence; and the incidence rate measures new cases over time.

The positive predictive value is the probability that a positive test result actually indicates the presence of disease. In practical terms, it answers: if the test comes back positive, how likely is it that the person truly has the disease?

PPV is calculated as true positives divided by all positive test results (PPV = TP / [TP + FP]). This value depends not only on the test’s accuracy (sensitivity and specificity) but also on how common the disease is in the population (prevalence). When the disease is rare, many positives can be false positives, lowering the PPV; when the disease is common, the PPV increases.

Why the other ideas don’t fit: the probability that a negative result means the disease is absent is the negative predictive value; the proportion of the population that has the disease is prevalence; and the incidence rate measures new cases over time.