Views & Reviews Personal View

Guidelines should reflect all knowledge, not just clinical trials

BMJ 2012; 345 doi: (Published 05 October 2012) Cite this as: BMJ 2012;345:e6702

Re: Guidelines should reflect all knowledge, not just clinical trials

The authors do make a pertinent point that all knowledge, whether it is derived from randomised trials or clinical experience, should be reflected in the guidelines.(1). But that does not mean that ‘the hierarchy of evidence’ need to be discarded.

To paraphrase George Orwell, ‘some forms of knowledge are more equal than others’. Knowledge from randomised trials is better than other forms of evidence. Widespread clinical and expert consensus cannot be accepted to be on par with evidence from randomised studies just for clinical expediency. ‘Groupthink bias’ presents a grave risk to the relevancy of clinical guidelines rather than the hierarchy of evidence. Randomised prospective evidence is the only real antidote to various biases.

I suspect ‘blood letting’ would have been unquestionably ranked the highest in the guidelines of the first millennium. Even in an 1871 BMJ article, there was a call for a "fair trial for blood-letting as a remedy".(2).

Contrary to authors’ assertion diagnostic aids, prognostic models and public health measures can be subjected to stringent prospective studies. Recent examples include studies of sugar-free beverages and a diagnostic aid to manage suspicious pigmented lesions.(3)(4)(5). Randomised prospective evidence should remain as the highest benchmark even though it is not possible to obtain such evidence in some clinical settings.


1. Zuiderent-Jerak T, Forland F, Macbeth F. Guidelines should reflect all knowledge, not just clinical trials. BMJ. 2012 Oct 5;345(oct05 4):e6702–e6702.

2. Blood Letting. BMJ. 1871 Mar 18;1(533):283–91.

3. de Ruyter JC, Olthof MR, Seidell JC, Katan MB. A Trial of Sugar-free or Sugar-Sweetened Beverages and Body Weight in Children. New England Journal of Medicine. 2012;367(15):1397–406.

4. Walter FM, Morris HC, Humphrys E, Hall PN, Prevost AT, Burrows N, et al. Effect of adding a diagnostic aid to best practice to manage suspicious pigmented lesions in primary care: randomised controlled trial. BMJ. 2012 Jul 4;345(jul04 1):e4110–e4110.

5. Wyatt JC, Altman DG. Commentary: Prognostic models: clinically useful or quickly forgotten? BMJ. 1995 Dec 9;311(7019):1539–41.

Competing interests: No competing interests

26 October 2012
Consultant Oncologist
Nottingham University Hospitals NHS trustt
Hicknall Road, Nottingham. NG5 1PB