What is evidence?

The term evidence is often used in a way that restricts its relevance to decision making, to the point of decisional irrelevance in many cases. Decisions must be, and are made, in both the clinical and public health contexts, whatever the state of the evidence by scientific standards. (The refusal to accept that not taking a decision now is itself a decision is an attractive delusion, but still a delusion.) It is common for those who are science-focused rather than decision-focused to grade the quality of evidence by scientific standards and we endorse this practice and indeed do it ourselves. But it is not helpful or appropriate to impose any threshold of acceptability on such grading; or to make statements, true but vague to the point of having no 'meaningful use', such as 'some evidence exists that...'The challenge for professionals in their daily practice is to translate such grades and statements into decision-relevant  magnitudes and we assume they accept this challenge and do it to the best of their ability and resources, especially time.  We do the same, merely insisting that the magnitude translation is into a number between 0 and 1. It is important not to cede rights over the term evidence to scientists and so we use it in relation to both the Ratings and Weightings. However we prefer to characterise what we seek to provide, on behalf of decision makers, as the Best Estimates Available Now (the BEANs). The 'E' is explicitly for estimates not evidence, since many are likely to say the best evidence does not meet their standards for what constitutes evidence.