The Cochrane Lecture. The best and the enemy of the good: randomised controlled trials, uncertainty, and assessing the role of patient choice in medical decision making.

This lecture aimed to create a bridge to span the conceptual and ideological gap between randomised controlled trials and systematic observational comparisons and to reduce unwanted and unproductive polarisation. The argument, simply put, is that since randomisation alone eliminates the selection effect of therapeutic decision making, anything short of randomisation to attribute cause to consequent outcome is a waste of time. If observational comparison does have any significant part in evaluating medical outcomes, there is a grave danger of "the best", to paraphrase Voltaire, becoming "the enemy of the good". The first section aims to emphasise the advantages of randomised controlled trials. Then the nature of an essential precondition--medical uncertainty--is discussed in terms of its extent and effect. Next, the role of patient choice in medical decision making is considered, both when outcomes can safely be attributed to treatment choice and when they cannot. There may be many important situations in which choice itself affects outcome and this could mean that random comparisons give biased estimates of true therapeutic effects. In the penultimate section, the implications of this possibility both for randomised controlled trials and for outcome research is pursued and lastly there are some simple recommendations for reliable outcome research.