Efficiency in testing refers to what percentage?

Efficiency in testing is defined as the proportion of true results—both true positives and true negatives—over the total number of tests conducted. This measurement effectively evaluates how well a test functions in identifying both conditions that are present (true positives) and those that are absent (true negatives).

When assessing the overall performance of a diagnostic test, considering both true positives and true negatives provides a more comprehensive picture of its accuracy. This means that a test's efficiency reflects its ability not only to correctly identify cases where the condition exists but also to accurately rule out cases where it does not.

By contrasting this with the other options, true positives only reflect one aspect of test performance and do not provide a complete picture. False negatives and false positives indicate cases of misclassification, which do not contribute to the test's efficiency but rather highlight its limitations. Therefore, the correct answer encapsulates the broad effectiveness of the testing method in correctly categorizing both the presence and absence of conditions being tested for.