The challenge of medical diagnosis: A primer on principles, probability, process and pitfalls.

Arriving at a medical diagnosis is a complex process, which requires clinical skill. However, the need for clear decisions has to be balanced by an acceptance of the ambiguity of many clinical situations. Complex presentations often require probabilistic inferences rather than presumed diagnostic certainty. The demands, logic and process of clinical diagnosis are highlighted. The multiple aspects of clinical reality and the impact of gold standards, nature of evidence and dichotomous disease/no disease categorization are discussed. The importance of population characteristics and context in diagnostics and prediction are emphasized. The statistics of agreement, Bayesian approach, certainty and risk, hazards and pitfalls, common errors, audit and the influence of commercialization on diagnosis are addressed. There is a need to formally teach the art and science of medicine and to transfer clinical skill rather than hope that such skills will be automatically imbibed during training.