ABSTRACT
This chapter looks at some length on the nature and function of diagnosis and reviews various means of achieving it. The human brain, being made of protoplasm rather than silicon, would - were it to function as a completely logical computer - take an impracticably long time to analyse and respond to a complex situation. As long as diagnosis is carried out by a human doctor, the observer effect, whereby the very act of observing changes what is perceived, simply will not go away. Given the enormous advantages that information technology has brought to the infrastructure and organisation of health services, there is every reason, one might think, to encourage computer-based thinking to infiltrate the clinical process. Those who like a rationalist approach to diagnosis yet are mindful of the inevitable uncertainties of clinical medicine are attracted to Thomas Bayes' theorem, which combines probabilistic thinking with the seductive rigour of the algorithm.
