Understanding evidence-based diagnosis.

The real meaning of the word "diagnosis" is naming the disease that is causing a patient's illness. The cognitive process of assigning this name is a mysterious combination of pattern recognition and the hypothetico-deductive approach that is only remotely related to the mathematical process of using test results to update the probability of a disease. What I refer to as "evidence-based diagnosis" is really evidence-based use of medical tests to guide treatment decisions. Understanding how to use test results to update the probability of disease can help us interpret test results more rationally. Also, evidence-based diagnosis reminds us to consider the costs and risks of testing and the dangers of over-diagnosis and over-treatment, in addition to the costs and risks of missing serious disease.