**Core Concept**
The confidence level of a test refers to the degree of certainty with which a test result can be interpreted. Increasing the confidence level of a test means that the test is more reliable and accurate in detecting a particular condition or disease.

**Why the Correct Answer is Right**
When the confidence level of a test is increased, it means that the test has a higher sensitivity and specificity. This is because the test is able to correctly identify more true positives (those with the disease) and true negatives (those without the disease). As a result, the positive predictive value (PPV) and negative predictive value (NPV) of the test will also increase. This is because the PPV is the proportion of true positives among all positive test results, and the NPV is the proportion of true negatives among all negative test results.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because increasing the confidence level of a test does not necessarily mean that the test will become more sensitive or specific, but rather that it will be more reliable in detecting a particular condition.

**Option B:** Incorrect because the confidence level of a test is not directly related to the number of false positives or false negatives. While a test with a high confidence level may have fewer false positives and false negatives, this is not the primary effect of increasing the confidence level.

**Option C:** Incorrect because the confidence level of a test does not affect the diagnostic yield of the test. The diagnostic yield is the proportion of patients with a particular condition who are correctly diagnosed by the test.

**Option D:** Incorrect because the confidence level of a test is not directly related to the cost or time required to perform the test. While a test with a high confidence level may be more expensive or time-consuming to perform, this is not the primary effect of increasing the confidence level.

**Clinical Pearl / High-Yield Fact**
Increasing the confidence level of a test can lead to improved patient outcomes by reducing the number of false positives and false negatives, and by improving the accuracy of diagnosis.

**Correct Answer:** C. The test will be more reliable in detecting a particular condition or disease.