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- Diagnostic testing, a term that encompasses physical examination, history, imaging techniques and procedures, as well as laboratory tests, provides the framework for clinical decision-making. A given diagnostic test is based on the assumption that diseased and healthy individuals can be accurately and reproducibly differentiated by the test (Knapp and Miller, 1992).

- Types of Diagnostic tests (Knapp and Miller, 1992):

i) Qualitative diagnostic tests classify patients as diseased or disease-free according to the presence or absence of a clinical sign or symptom. For example, an x-ray might confirm or disprove the existence of a fracture.

ii) Quantitative diagnostic tests classify patients as diseased or disease-free on the basis of whether they fall above or below a pre-selected cutoff value known as the positivity criterion. This cutoff value is also referred to as the critical value or referent value.

- The following Website may help you if you are new to the concept of validating diagnostic tests.

http://bmj.com/cgi/content/full/315/7107/540