Do evaluation principles apply the same for screening and diagnostic tests?

• A. They are the same in evaluation and interpretation
• B. They are completely different
• C. They have no common principles
• D. They require different thresholds for prevalence

Answer: (A)

The key idea is that the same evaluation framework applies to both screening and diagnostic tests. The measures that describe how a test performs—sensitivity, specificity, likelihood ratios, and predictive values—are intrinsic to the test itself and are used to judge accuracy in any context, whether you’re screening a population or confirming disease in an individual.

In practice, the use of those measures differs by context. Screening aims to detect as many true cases as possible in a mostly healthy population, so there’s a tendency to favor high sensitivity and to rely on a follow-up diagnostic test for positives. Diagnostic testing is usually performed in people with higher pretest probability, so specificity becomes very important to avoid false positives. Predictive values shift with prevalence, but the fundamental principles governing test performance remain the same.

So evaluation principles apply in the same way for screening and diagnostic tests.