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Dear Kev, Thank you, this was beautifully explained and very helpful.. Amy From: Evidence based health (EBH) [mailto:[log in to unmask]] On Behalf Of k.hopayian Sent: Monday, October 17, 2011 3:45 PM To: [log in to unmask] Subject: Re: Systematic reviews of qualitative studies Hi Kathleen, Looking back over how these have developed over the years, this is my summary of the situation (based on memory and observation, not detailed historical research). Hierarchies of evidence and levels of evidence have been proposed by different groups, at different times, in different forms and for different purposes. Most rankings use them to rate the strength of evidence, for example the Scottish Intecollegiate Guidelines Network (your neck of the woods, I think); it gives a worked example on http://www.sign.ac.uk/guidelines/fulltext/50/compevidence.html. The Centre for Evidence-Based Medicine has argued that the purpose is to assist the seeker of evidence to find a shortcut to the best evidence, http://www.cebm.net/index.aspx?o=5513 but as in all but one case, systematic reviews count higher than single studies, it is hard to see how this differs from the other groups's aims. There has been a growing realisation within EBP that in the early days, too much emphasis appeared to be placed on RCTs. This was understandable given the interest in studying interventions. As EBP has matured, there has been a more balanced appreciation of other study designs. I believe that the common themes that run through all the different systems today are: 1. Some questions are better answered by certain study designs than by others. It is important to choose the best study for the type of question. (So you are right to say that RCTs are ranked above cohort studies for intervention questions. However, a long term cohort study might give better information about long term adverse effects or about prognosis). 2. Synthesised evidence (a systematic review) ought to give more reliable information than a single study but this depends on the quality of the review and of the primary studies. One example I like to use is of a systematic review that pooled data from several old, poor quality studies and from the newest high quality study - in that case, in my opinion, the single RCT was better than the SR. 3. It is not sensible to put one type of SR (e.g. of cohort studies) above another type (e.g. qualitative studies) because they relate to different questions. You might as well ask, what is the best thing to do for a DVT, ultrasound or warfarinisation? Dr Kev (Kevork) Hopayian, MD FRCGP General Practitioner, Leiston, Suffolk Hon Sen Lecturer, Norwich Medical School, University of East Anglia GP CPD Director, Suffolk Surgery Tel +44 1728 830526 Surgery Fax +44 1728 832029 [log in to unmask] http://www.angliangp.org.uk/ Making your practice evidence-based http://www.rcgp.org.uk/bookshop On 17 Oct 2011, at 19:47, Kathleen Irvine wrote: That surprises me. Don't hierarchies distinguish between systematic reviews of RCTs, those of cohort studies, those of case control series....all of which are considered as operating as different levels of evidence? From: [log in to unmask] [mailto:[log in to unmask]] On Behalf Of Susan Fowler Sent: 17 October 2011 18:42 To: Kathleen Irvine Cc: [log in to unmask] Subject: Re: Systematic reviews of qualitative studies Most hierarchies of evidence I see don't distinguish between a systematic review of quantitative vs qualitative studies. I would think if it is a systematic review of qualitative studies it is still a systematic review and thus still in the same place as other systematic reviews on the hierarchy of evidence. -- Susan Fowler, MLIS Medical Librarian Evidence at Becker: http://beckerguides.wustl.edu/ebm Mobile Resources Guide: http://beckerguides.wustl.edu/mobileresources Becker Medical Library, Washington University in St. Louis 314-362-8092 [log in to unmask] On Mon, Oct 17, 2011 at 12:25 PM, Kathleen Irvine <[log in to unmask]> wrote: Can anyone advise how systematic reviews of qualitative studies should be regarded in terms of evidence-based practice? They don't have a place on the normal hierarchies of evidence but often seem to be of potential value to clinicians. Kathleen Irvine Subject Librarian Highland Health Sciences Library University of Stirling Highland Campus Centre for Health Science Inverness IV2 4AG (01463) 255608 _____ The Sunday Times Scottish University of the Year 2009/2010 The University of Stirling is a charity registered in Scotland, number SC 011159. _____ The Sunday Times Scottish University of the Year 2009/2010 The University of Stirling is a charity registered in Scotland, number SC 011159.