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It is through clinical reasoning that clinicians collect, weigh, and combine the information required to reach diagnosis; decide which treatment is required; monitor treatment effectiveness; and change their plans if treatment does not work. The study of clinical reasoning, therefore, concerns the cognitive processes that underlie diagnosis and the planning and implementation of treatment.

Diagnosis has three purposes: to aid research, to summarize information, and to guide treatment. For clinicians, the chief purpose of diagnosis is to summarize information in such a way as to guide treatment. In one approach to diagnosis, the clinician matches a pattern of clinical phenomena elicited from the patient against the idealized patterns of disease entities and chooses the diagnosis that best fits. In another approach, the clinician attempts to understand the particular environmental, biological, psychological, and existential factors that have both led to the current problem and perpetuated it. The first approach, therefore, seeks commonality and lends itself to generic treatment planning. The second approach stresses uniqueness and the adaptation of treatment to the individual. In good clinical practice, the two approaches are complementary.


Diagnosis and treatment are risky ventures, fraught with the possibility of error that can have serious consequences. How can error be minimized? On the one hand are the clinicians who, having elicited information that is generally both incomplete and inferential, diagnose patients and use subjective probabilities to predict outcome. On the other hand are the psychological actuaries who regard natural clinical reasoning as so flawed as to be virtually obsolete and who seek to replace it with reliable statistical formulas.

A considerable amount of research has been conducted into the fallacies and biases that can lead clinicians astray. For several reasons, such research has had little effect on clinical practice. Actuarial experiments sometimes seem artificial, or even rigged (against the clinician), and may be dismissed as irrelevant. Clinicians are prone to concede that others may make a particular mistake in reasoning while maintaining that they themselves are unlikely to do so. Indeed, clinicians often have a degree of self-confidence that enables them to survive in an uncertain world, and they are not likely to accept their defects unless they see a practical remedy. Finally, clinicians may fear that, if tampered with, their mysterious diagnostic skills will evaporate and be replaced by computing machines.


There are three types of research into clinical reasoning: clinical judgment, decision theory, and process tracing. Clinical judgment research attempts to identify the criteria used by clinicians in making decisions. Decision theory explores the flaws and biases that deflect accurate clinical judgment. Process tracing elucidates the progressive steps of naturalistic reasoning. The first two types are statistical and prescriptive, the third is normative.



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