Diagnostic Process, Making a Diagnosis

Methods of Diagnosis

How physicians make a medical diagnosis has received considerable study and attention, although our understanding remains incomplete. Traditionally, physicians were thought to first systematically collect a complete clinical data set on the patient. This included the chief complaint, the history of present illness, the patient's complete past medical history, the patient's social history, a detailed family history, a comprehensive review of systems, and, finally, the complete physical exam. Only as a second and separate step were physicians thought to analyze the data and diagnose the responsible disease.

Despite the belief of some physicians that this method is central to diagnostic success, when psychologists study the process of diagnosis, they find that expert physicians do not blindly collect clinical information. In fact, expert physicians are often observed to collect less information than novice physicians when making diagnoses but are much more likely to make the correct diagnosis. While the novice physician collects a great deal of information, the novice can miss collecting the data needed to make the diagnosis. Expert physicians might be expert in knowing which data to collect as well as expert in knowing which data are irrelevant to the diagnostic task.

It appears that physicians use intuition, deliberate reasoning, or a combination of these two processes when engaged in making medical diagnoses. Many psychologists describe two different and complementary mental systems used by humans: [Page 380]an automatic, experiential, recognition-based system and a rational, conscious, analytic system. The recognition-based system generates impressions of the attributes of objects of perception and thought. These impressions are not necessarily voluntary and often cannot be explained by the person. In contrast, the conscious, analytic system involves deliberate reasoning, which is much slower and effortful but more controlled. Although these two cognitive systems operate independently, there is reason to suspect that skilled diagnosticians learn to use their analytical brains to double-check their intuitive brains. In the discussion below, three distinct diagnostic methods are presented. These are presented as prototypes; physicians might use one of these three methods and a mixture of these methods when involved in medical diagnosis.