Definition: A diagnostic test is a procedure which gives a rapid, convenient and/or inexpensive indication of whether a patient has a certain disease. All diagnostic tests have four possible outcomes:

1. the test is positive, and the patient has the disease (true positives);
2. the test is positive, and the patient does not have the disease (false positives);
3. the test is negative, and the patient has the disease (false negatives);
4. the test is negative, and the patient does not have the disease (true negatives).