Guidelines should reflect all knowledge, not just clinical trials

Over the past 20 years, evidence based medicine has had a substantial influence on clinical decision making throughout the developed world. It now underpins healthcare policy and the burgeoning industry of clinical guideline development. Two problems have resulted. Firstly, so called high level evidence is increasingly equated with strong recommendations; and secondly, evidence other than that derived from randomised controlled trials (RCTs) is seen as intrinsically less valuable or reliable.

The concept of a hierarchy of evidence with RCTs at the top is deeply ingrained, despite Sackett and colleagues’ warning that evidence based medicine “is not restricted to randomised trials and meta-analyses. It involves tracking down the best external evidence with which to answer our clinical questions.”1 They pointed out that RCTs and systematic reviews of RCTs will provide the most reliable evidence that a therapy will do more good than harm but acknowledged that “some questions about therapy do not require randomised trials (successful interventions for otherwise fatal conditions) or cannot wait for the trials to be conducted.”

They also made clear that other questions, such as those about diagnostic tests and prognosis, can only be answered using other forms of evidence. In his 2008 Harveian oration, Michael Rawlins, chairman of the National Institute for Health and Clinical Excellence (NICE), elegantly analysed the strengths and …