Severity scores in surgery: what for and who needs them? An introduction: definition, aims, classification and...

Every patient represents a unique and complex situation a clinician has to deal with. In order to cope with this complexity of information, reduction is necessary, especially in communication about diseases or therapy. The first reduction is made when a patient is given a diagnosis which reflects a constellation of similar symptoms. A score also reduces the given amount of clinical data into a one-dimensional value. The primary aim of a score is a systematic comparison between patients and institutions. Scores reduce information to focus on the essentials. They are used for severity classification and prognosis, evaluation of outcome and treatment effects, case-mix adjustments in comparative audits, and economic evaluation. Quality criteria of score systems which should be considered in the development and application are: reliability, validity, measurability, applicability, and clinical relevance. This introductory article gives a brief description of these terms.