How does switching to parallel interpretation affect overall sensitivity and specificity?

• A. In parallel interpretation, both sensitivity and specificity increase
• B. In parallel interpretation, sensitivity decreases and specificity increases
• C. In parallel interpretation, sensitivity increases and specificity decreases
• D. In parallel interpretation, both decrease

Answer: (C)

Switching to parallel interpretation means a person is labeled positive if any one of the tests comes back positive. This increases the chance of catching true disease cases, so overall sensitivity goes up. But this broader net also sweeps in more people without disease who test positive on at least one test, raising false positives and lowering specificity.

For example, if two tests each have sensitivity of 0.80 and specificity of 0.95, the parallel approach yields a combined sensitivity of 1 − (0.20 × 0.20) = 0.96, while the combined specificity becomes 0.95 × 0.95 = 0.9025. So you gain sensitivity but lose specificity.