Which metric specifically measures the proportion of truly diseased individuals who test positive?

• A. Specificity
• B. Predictive Value Positive
• C. Sensitivity
• D. Validity

Answer: (C)

The main concept is sensitivity, which is the test’s ability to identify disease among those who actually have it. It answers the question: among people who truly have the disease, what fraction will test positive? It’s calculated as true positives divided by true positives plus false negatives. This focuses on catching disease when it’s present, which is exactly what “proportion of truly diseased individuals who test positive” describes.

Specificity, by contrast, looks at people without the disease and asks how many test negative they are, not how many diseased people test positive. Predictive value positive combines the test result with the prevalence of disease to answer the probability that someone with a positive result truly has the disease, which depends on how common the disease is in the population. Validity is a broader term and not a specific measure like sensitivity.