Assessing Diagnostic PerformanceDiagnosis is an action and a goal in medicine. This article is the introduction to a series of review articles on varying facets of diagnosis. Clinical diagnosis is an exercise in classification; that is, placing the patient's condition in the correct diagnostic category. However, consideration must also be given to the performance objective, whether it is technical performance of a test, acquiring diagnostic information with respect to clinical management for an individual or a population's health outcomes, or cost-effectiveness and equity of care.