Conceptual issues in computer-aided diagnosis and the hierarchical nature of medical knowledge.

Attempts to formalize the diagnostic process are by no means a recent undertaking; what is new is the availability of an engine to process these formalizations. The digital computer has therefore been increasingly turned to in the expectation of developing systems which will assist or replace the physician in diagnosis. Such efforts involve a number of assumptions regarding the nature of the diagnostic process: e.g. where it begins, and where it ends. 'Diagnosis' appears to include a number of quite different cognitive processes, some of which seem more subject to formalization than others. Underlying the difficulties inherent in these efforts at formalization, is the hierarchical structure of medical knowledge including that of diseases. (By 'hierarchical structure', I mean no more than that our descriptions of clinical objects necessarily refer to different levels of organization; atomic, molecular, cellular, physiological system, entire patient). Since diagnosis is in part a form of classification, measures of similarity between the clinical findings of a particular patient and a potential disease, are needed. This is complicated by the fact that some diseases are described using the vocabularies of physics and chemistry, others with the vocabulary of psychology, and most, with terms taken from a number of different hierarchical levels. The differences between the descriptions made using these vocabularies will be seen to exert systematic (if not uniform) influences upon the diagnostic process.