Evidence based medicine or evidence based clinical practice is the judicious application of best current knowledge to the condition and values of the individual patient. Evidence can also be used for groups of patients or populations and the terms used to describe these activities vary from one document to another, sometimes being called evidence based health care, evidence based management, evidence based public health, or evidence based policy making. An example of evidence based policy making is the United Kingdom's decision to introduce screening for Down's syndrome.1 2 The common feature to all these debates is the use of evidence to make decisions about groups of patients or populations.

Evidence based policy making sets the context in which evidence based clinical practice can take place. If the policy is not to offer screening for breast cancer to women under the age of 50, the clinician does not have to interpret the evidence about the benefits and harms of screening such women. Critics say that this is a form of rationing. …