**Core Concept**
Specificity of a screening test is a measure of its ability to correctly identify individuals who do not have the disease. It is a crucial parameter in evaluating the performance of a diagnostic test, particularly in high-prevalence populations where false positives can lead to unnecessary harm.

**Why the Correct Answer is Right**
The correct answer measures the proportion of true negatives among all actual negatives. In other words, it estimates the probability that a test result is negative in the absence of the disease. This is essential in clinical decision-making, as it helps clinicians to avoid unnecessary treatments and interventions. Specificity is closely related to the concept of false positives, which can lead to decreased patient trust and increased healthcare costs.

**Why Each Wrong Option is Incorrect**
**Option A:** Sensitivity measures the proportion of true positives among all actual positives. While sensitivity is an important parameter, it is not related to specificity.
**Option B:** Positive Predictive Value (PPV) estimates the probability that a test result is positive given the presence of the disease. PPV is affected by both sensitivity and prevalence, but it is not a direct measure of specificity.
**Option C:** Negative Predictive Value (NPV) estimates the probability that a test result is negative given the absence of the disease. NPV is related to specificity, but it is not the same measure.

**Clinical Pearl / High-Yield Fact**
A high specificity does not necessarily imply a high sensitivity. In fact, it is possible to have a highly specific test with low sensitivity, which can lead to missed diagnoses. Clinicians should carefully evaluate both sensitivity and specificity when selecting a screening test for a particular population.

**Correct Answer: D.**