Introduction

Doctors constantly make decisions that affect the health and lives of other people. They gather evidence by interpreting the signs and symptoms of the patient, conducting examinations and determining appropriate tests. All of these actions imply the use of judgement and decision-making. Using such evidence they may form a diagnosis and conclude what, if anything, is to be done. In the current healthcare climate, patients are also encouraged to participate in decision-making, either by sharing in it, or by making their own informed decisions, on the basis of the evidence presented to them by doctors (Charles et al., 1997). Many of these decisions will be based on clear evidence from the patient and tried and tested methods drawn from the doctor's medical knowledge and may seem quite straightforward. However, very often, simple medical principles and rules will not be available. From the perspective of formal Decision Analysis, in order to make an optimal decision, a doctor and patient must identify all the options available, work out their potential outcomes and the probability that these outcomes will occur. They also need to assess how good or bad that outcome occurring would be. Such a process is often difficult for several reasons. Firstly, it is difficult to identify the options and outcomes and their associated probabilities. As the evidence base of medicine develops this may become easier, but where clear evidence about options, or actuarial statistics about their outcomes, are not available doctors have to rely on their judgement.