Project Methodology 5

Health Evidence Bulletins - Wales (logo)

TYPE OF EVIDENCE CLASSIFICATION
FOR THE HEALTH EVIDENCE BULLETINS - WALES*

I Evidence from a systematic review (which includes at least one randomised controlled trial and a summary of all included studies).
Examples include those published by the Cochrane Collaboration, the NHS Centre for Reviews and Dissemination and NICE.  The evidence from such a review requires careful appraisal as, if well done, the evidence is powerful.
 
II 

Evidence from a well designed randomised controlled trial of appropriate size.
 

III Evidence from a well designed intervention study without randomisation.
Evidence in this category will only be included if no category I or II evidence is available.  A common research design is the before-and-after study.
 
IV Evidence from a well designed non-experimental study  e.g. cohort, case-control or cross-sectional studies. (Also include studies using purely qualitative methods)
Evidence in this category will only be included if no category I, II or III evidence is available.  Economic analyses (cost-effectiveness studies) are also classified as Type IV evidence.
 
V Opinions of respected authorities, based on clinical evidence, descriptive studies or reports of expert consensus committees
 

*  This classification is based on the Bandolier system (http://www.jr2.ox.ac.uk/bandolier/band6/b6-5.html) adapted to include the NHS Centre for Reviews and Dissemination criteria for a systematic review (see the Database of Abstracts of Reviews of Effectiveness in the Cochrane Library).

 

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