Diagnostic reasoning and treatment planning: I. Diagnosis.

Information-processing research into the natural process of clinical reasoning is reviewed and the University of Vermont diagnostic reasoning research project is described. Experienced psychiatric diagnosticians use a hypothetico-deductive logic. The development of a profile of diagnostic competencies is outlined and a course in diagnostic reasoning for medical students, which specifically objectified the tactics and strategy of reasoning and resulted in a significant improvement in the profile of competencies, is described. Finally, the organisation of a diagnostic formulation is discussed.