Advances in Health Sciences Education

, Volume 2, Issue 2, pp 173–184

The Non-Analytical Basis of Clinical Reasoning


  • Geoffrey R. Norman
    • Health Science CenterMcMaster University
  • Lee R. Brooks
    • Health Science CenterMcMaster University

DOI: 10.1023/A:1009784330364

Cite this article as:
Norman, G.R. & Brooks, L.R. Adv Health Sci Educ Theory Pract (1997) 2: 173. doi:10.1023/A:1009784330364


This paper explores the assertion that much of clinical diagnostic thinking is based on the rapid and unconscious matching of the presenting problem to a similar, previously encountered, problem. This ‘non-analytic’ form of concept formation has been described in the psychology literature for over a decade. From this theory, we deduce and test several hypotheses: 1) Diagnosis is based in part on similarity to a particular previous example. In studies in dermatology, specific similarity accounts for about 30% of diagnosis. 2) When experts err, these errors are as likely as novices to occur on typical presentations. For residents, general practitioners and dermatologists, about 40% of errors were on typical slides. 3) Features are re-interpreted in light of diagnostic hypotheses. In radiology, attaching a standard positive history to the film bag increased the number of features seen on both normal and abnormal films by about 50%. 4) Experts cannot predict errors of other experts. In dermatology, experts predicted only 11–60% of errors committed by their colleagues. We conclude that amassing prior instances is an important component of expertise, and education should recognize this element.

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© Kluwer Academic Publishers 1997