Norma e caso individuale nella diagnosi medica: stili di ragionamento

This paper analyzes the relation between rule and exception by examining two approaches to clinical diagnostic reasoning. The first is based on regularities: a set of signs and symptoms is explained, or classified, by an appeal to the (statistical) regularities that point to certain pathologies as the most probable causes, or nosographic labels, of that set. The second approach makes a substantial use of analogy: the diagnostic question is solved by finding one or more previously observed cases that are similar to the one under investigation. In information technology, the distinction between the two approaches becomes apparent in the area of decision support systems, where we find two different architectures based, respectively, on Bayesian networks and on case-based reasoning. I connect the problems emerging from these approaches to current philosophical discussions on the foundations of Evidence Based Medicine and on the topic of generic and singular causation.